Tidy all the junk from your desk into a convenient portable box with an integrated USB charger.

Use the storage compartments on the top of the box for small change, USB keys etc, and the removable tray for pens, USB dongles, loyalty cards and whatnot.

A mains-powered USB charger in the base can charge your phone, bike lights or whatever. When you are done topping up, tuck the charging cables back inside & close the lid, unplug, and your desk accoutrements are portable.

If you need more space, you can always upgrade to a bigger toolbox later.

A ten minute job, and you might well already have all of the things that you need.

Step 1: Go Shopping

The links are to Amazon for convenience. You'll need the following:

a plastic toolbox — eg Stanley Plastic Toolbox 16" – local hardware supplier
a USB charger that will fit inside your toolbox, with a mains cable (ie not one with an integrated plug!)
a replacement wall plug for your USB charger
You'll also need these, or functional equivalents:
a hole reamer to make a hole in your box for the charger power cable
a screwdriver and a wire stripper to change the plug
assorted USB charging cables—the squid ones are handy

Step 2: Measure for the Cable Hole

Remove any tray from the box, and place the charger in.

Mark on the inside of the box where you want the hole for the cable.

Step 3: Make the Hole for the Cable

Use the reamer to make a small hole for the cable. Err on the small side; you can always make the hole bigger, but once it's too big there's no going back.

If you don't have a reamer you could make the hole with a steel drill bit, or your second-best soldering iron. Work from the outside so that it looks neat.

Step 4: Fit the Cable

Using your wire cutter or a pair of pliers, cut off the supplied moulded plug—the mains end, not the charger end—that came with your USB charger. Remove and retain the fuse from the plug.

Thread the cable through the hole you made from the inside of the toolbox, ie with the cut end on the outside. If the hole's too tight, embiggen it a little.

Step 5: Attach Your Plug

Replace the fuse in the new plug with the one from the plug that came with your USB charger.

Using your screwdriver and your wirecutter or pliers, fit your new plug on the end of the cable. UK plugs normally come with a paper pattern for cutting and stripping the cables—if in doubt, you'll find detailed instructions elsewhere on Instructables. Double-check that you have done this properly, mains power is potentially dangerous.

Step 6: Connect It All Together

Plug your charger in to its cable and sit it in the bottom of your toolbox. If you turn the charger so that the power cable has to go back across it, this provides some stress relief that helps prevent the power cable pulling out if there's any tension—that's what the Velcro cable tidy is doing.

Connect the plug to a wall socket and turn it on; the power LED on the charger should light up.

Add your charging cables and connect your devices ?

Put the tray back in, and tidy up.

I haven't noticed any significant heat build-up in the toolbox, but even with a 3A fuse 240V is capable of significant power. It's probably best to: