Chums can wear two pieces of gear at any time. You can purchase hats and things for your chum to hold. New gear is available as you level up. In the store you can try on all gear. (Even if it requires a higher level) Just tap on any items picture to see it on your chum. Gear looks cool and boosts the rate at which you earn experience (XP). Take a look at the Experience section of help for more details.

Energy doubles the rate at which you earn experience. You can buy as much boost as you want and it will add to your boosted time.

You can also stock up on Hints and Bombs.

You can always buy more Chums or different colors of Chums. When you buy a new Chum the old Chum/color combination will still be in your inventory and you can always switch back to it.