@al1's battery box tip
LiPos have their special place in many of our projects, but sometimes it's just neat to have one of those AAA battery boxes with a switch that fits two-three batteries. Many of the common projects run just fine off them, like @al1 's #reCLOCK -> it's so tiny! But it also helps to show off the piece, because it makes it portable.
@Radomir Dopieralski's two cents
A. Make sure the batteries are easily removable, and take a few spares and a charger. This way you can charge one battery while the project runs on the other.
B. Remember that your projects are probably not designed to move all the time for 8+ hours straight. Motors get hot, servos wear out and break, batteries can only take so much recharging. So make breaks. If you have several projects, run one at a time. This will also encourage people to come back to your table later.
Use USB hubs and breadboards
Kind of obvious, but in case you want to power a lot of little projects, you can easily distribute power with a USB hub or use breadboards. Powered USB hubs should work pretty well, but you can also put HUBs on power banks!