Long time reader, first time poster. I'm a software engineer but a noob at hobby electronics, so bear with me if I make mistakes :) I'm learning as I go.

I saw a couple different projects here that I found interesting:

https://www.instructables.com/id/Supercapacitor-USB-Light/

https://www.instructables.com/id/LED-Zippo-Flashlight/

I thought both were really cool but I thought it might be cool to combine them. I wanted a zippo LED flashlight that could be recharged quickly using a widely available and convenient power source: USB. Since most cell phones use micro USB cords for power I figured that would be a good source for my project as well.

Step 1: Get Parts Ready

For parts, I used:

-Zippo lighter
-three 0.1 Farad supercapacitors (found on Amazon)
-one 10 ohm resistor
-one 1K ohm resistor
-one temporary pushbutton switch (from Radio Shack)
-one standard LED (of whichever color you prefer)
-one microUSB breakout board from Sparkfun

Tools:
-Needlenose pliars
-Cordless drill with various bit sizes
-Hot glue gun and glue
-Soldering iron and solder
-22 gauge wire

Step 2: Prepare the Zippo

I apologize, I decided to do the instructable after I had completed the project so I don't have pictures of these intermediate steps, so you'll have to bear with my description.

First, remove the zippo from the package. Open it and pull the inside part out as if you were going to refill it if you were going to use it as a real lighter. Remove the cotton stuffing inside and pull out the wick.

On the one side will be a brass tube with a screw at the end. Unscrew it. A spring and the flints should come out. You can discard those, we won't be needing them.

On the top of the lighter is the wheel (what we'd spin to spark the flint to start the lighter). Use your needlenose pliars to slightly bend the metal flaps on either side outward so that the wheel comes free. You can discard the wheel. Bend the flaps inward toward where the fire would be so that the top of the fire area is an enclosed "cage". (see the main photo so you see what I did with these flaps)

Inside the center piece, the brass tube we discussed earlier is usually glued against the inside of the top where the flint/wheel used to be. Use a dremel or the power drill and CAREFULLY remove as much of the glue as possible. The metal in the zippo is quite thin, so you have to be very careful what you're doing so you don't drill right through to the other side. Once a significant amount of the glue is removed, take your needlenosed pliars and in the bottom of the center piece, grab the brass post. Firmly but slowly rock it back and forth until it breaks free from the upper section leaving a hole where the flint would have passed through to the wheel on the top. Now, take a drill bit that is as close as possible to the size of the barrel of the pushbutton switch and carefully drill through that hole to clear any debris. Try fitting the pushbutton switch up through this hole. If it doesn't fit, use a slightly larger drill bit and repeat. (It may take several attempts to get this right.)

Step 3: Make Your Circuit

First, solder wires onto the leads of your LED. Remember, it will stay inside the "cage" at the top of the lighter where the fire would be, so make sure that your leads are bent/short enough that the LED doesn't stick out over the top of the cage very much (or at least make sure the top of the zippo can close). Thread the wires down through the hole where the wick was (I didn't need to modify the side of this hole at all, the 22 gauge wire fit just fine). Make sure the wires are long enough that you'll be able to solder them to the rest of the components.

Solder wires onto the leads of the pushbutton switch. As with the LED, make sure the wires (if the pushbutton is in place) are long enough that you'll be able to solder it to the other components.

Using the diagram included here, solder the circuit in this manner:
-MicroUSB positive input to the positive wire for the pushbutton switch
-Negative wire of the switch to the positive on the LED
-Negative of the LED to the 1K resistor
-1K resistor to ground on the microUSB
-solder the capacitors in parallel
-solder the 10ohm resistor to the positive input from the microUSB
-solder the 10ohm resistor to the positive input for the parallel capacitor group
-solder the negative side of the capacitor group to the ground on the microUSB

I covered some parts of the components with electrical tape to insulate them from each other and from the outer casing of the lighter. In addition, I put a strip of electrical tape at the bottom of the outer casing to insulate the microUSB plug from the outer casing (not sure if necessary but I wanted to be careful).

Some tips:
-make everything as tight as possible. I did everything WAY too loose and had to cram everything in there at the end and it barely fit. Like really really close to not fitting.
-try soldering the capacitors in an alternating fashion in the group (kind of how they're shown on the parts page) to save space. Mind the polarity though! So one on one side, one on the opposite side, then the third on the same side as the first.

Step 4: Test!

Plug a microUSB cable into the microUSB port and into a USB power source (computer, etc).

Give it 10 minutes.

Unplug it and then push the pushbutton switch and see if the LED turns on. If so, you're golden. If not, check your soldering.

Step 5: Finalize

If everything works, use your hot glue gun to fill in the gaps around the microUSB breakout board in the bottom of the zippo's center piece (see picture). Make extra sure you don't accidentally get hot glue in the actual microUSB port itself or you won't be able to charge it in the future.

When you're done it should look something like the second picture below.

Step 6: You're Done! :)

So, at this point, if the LED lights you should be golden :)

I had tested this before finishing everything and if you give it 10 minutes to charge, it will stay powered for about an hour of continuous bright light, and several hours more of progressively dimmer light. I also tested it by leaving it dormant and checking it once a day for a week and it stayed pretty useful for almost all of that time.

Some notes:

-I'm a noob, so I'm sure there are probably better/more efficient choices for components for this project. I'm learning as I go, and I found something that worked and ended up with performance pretty much what I had hoped for at the beginning of this venture.

-A friend had voiced concern about the capacitors being overcharged or something... He didn't have a specific belief that it would happen, but was asking if I had looked at that as a possibility. I hadn't and I'm not an expert on supercapacitors. That said, I've tested it many times by charging at ranges from 5-20 minutes and haven't had an explosion yet, so I'm assuming it's fairly safe. However, undertake this project at your own risk. I accept no responsibility if you blow up your hand or something. ;)

-I wish I could have gotten it to work properly with two LEDs... No matter what I tried, I couldn't get a decent level of brightness with two. So I finally decided to stick with one, which gave decent brightness and good longevity.

-It's not perfect, but it's a fun little project and practical. :)