I am a hiker. Sometimes I dayhike, sometimes I overnight (mostly on longer trips). But this is my passion. This is my list of what you need for a dayhike during late spring/summer. Add what you want to what you bring also, because I'm sure I missed a few things.
Step 1: The Pack
For the pack, the carrier of all of your equipment, this needs some thinking over. How big will it be? Will it be technical or just a trail pack? Think about what you do, and choose on that. This pack is a REI Traverse 30, a technical pack. It was $60, an amazing deal. Most daypacks don't go over $150, but if yours does, it might be a bit to expensive. Your choice, though.
Step 2: Hydration
Hydration is the most important thing to have. It can be a water bottle or a hydration bladder, you need it. In this case I have a hydration bladder. Most packs have a compartment for it by the suspention, but if it doesn't, you don't really need it. The water bottle carries less water but is tougher. I usually carry both. If you are going to buy a hydration bladder, don't pay more than $60 for it.
Step 3: Knives/Multitool
This area is the most broad, from little pocket knives 2 inches long to sheath knives the size of my hand to elbow, or multitools that carry only a file to those that have enough tools to fix a car and change its oil (please catch that sarcasm), there are many varieties of both. Here I have a bone handled sheath knife that is about 6 inches long. Please don't laugh at the look of it, because it has saved me in many situations. They are very trusty knives. On the top I have a modern Gerber multitool, with locking tools that are VERY strong. Bad thing-its really heavy. Below it is a classic Leatherman, one of my favorite camping items. It has very basic tools, pretty much all you would need. It is also pretty lightweight.
Step 4: Rope
Pretty self explanitory, on the top is a survival bracelet that has 8 feet of paracord on it. Bottom has roughly 50 feet of paracord. I would recommend having 50 feet of paracord for climbing down cliffs, ect.
Step 5: Matches
Also pretty self explanitory. Use matches to start a fire. BE CAREFUL!!! Also carry candles, they can be useful (just don't eat them).
Step 6: Food
Food is a must. Bring granola bars, power bars, or any other high energy bar. Also, you might want to bring a candy bar (not in pictures) such as a Snickers bar. Hard candy is nice to have so you can have something to suck on as you hike. Just remember to throw away the wrapper correctly. Tasty!
Step 7: Light
There are thousands of types of lights you can use, from head lamps to giant police lights. I like pen lights and head lamps, very lightweight. Here I have a pen light. Without a light, you can become disoriented and lost, thus a rescue team to pick you up. And you don' want that.
Step 8: Ziplocs
I always bring along a very fancy water tight bag called a Ziploc. I put matches, knives, or other things that can't go in water into them. Always carry a few with you, they have many uses.
Step 9: Other Things
Other things you can bring with you that are nice to have
Camera- you never know what you will see
Paper and Pen- Keep notes of your travels
Watch- Whats the time?
Step 10: Enjoy!
Now go explore the giant thing we call earth. With all of these items, the world is your oyster.