There are all sorts of boxes you find throughout the game that give you different results when you hit them.

wood - random bolts
red - exploding box
blue sphere - health
G - random weapons (usually what you need)
flames - inferno (temporary boost to armor, with dual-wrench flaming power)
? - jackpot crate, temporarily multiples experience. Slay things quickly when you have this!

Ratchet and Clank 3 - Up Your Arsenal Walkthrough