Set up a 'pot'. A set proportion of earnings from shows and other related things goes into the pot to be spent only when there is a general consensus that it is strictly necessary.
My old band did this - we'd put together money from gigs to upgrade the gear. We started off with a £3000 loan and bought a Transit van (£1200), a Mackie 1000w PA (£1200 at trade cost) and £500 for a lighting rig. The other £100 went on mic stands and a few beers. That got us on the road so we could make money gigging (we already had some other gear between us from previous bands like a mixing desk, leads etc...)
Bit by bit we gradually got specific mics for the cabs (D112 and SM57), mics for the drums (D112, SM57, Groove Tube GT-55s) and Shure Beta58 vocal mics.
We got some outboard to make our sound punchier - 6 channels of compression/limiting/gating and a reverb unit to sprinkle some sauce on the vocals when needed. Oh, and there was two channels of 31-band EQ that was used to shape the kick and snare sounds through the PA.
That same 'pot' of money paid for a lighting rig, monitors, smoke machines and a rehearsal room we rented out for our sole use 24/7.
:twisted: