Neat little game - like the variety of the different weapon.
Things i'd like to see as an improvement, would be auto loot / magnetic force to loot the items (at least at the end of a wave) and that self-inflicted damage is only active when an enemy wave is currently active. May feel a bit punishing trying the newly purchased weapon out before starting the wave, only to start over again.
Overall i had fun, good job for your first game jam.