A messy backpack can be more troublesome than the creatures coming at you. The trick is reshuffling your gear quickly enough to keep the useful stuff within reach before the next wave closes in. Currency Multiplier, Fast Forward, and No Ads are already unlocked in the current version, making resource runs and progression much smoother.
The charm comes from that slightly frantic inventory juggling. A tidy setup can become useless after a few new weapons land in your slots, and eventually the way you arrange the bag starts to feel like part of the combat itself.