Year 1: We purchased a SoundMachine system for talking to the band during rehearsals. Ended up using it with a couple mics the first year for some solos.
Year 2: Yamaha Mixer (Analog 16 Channel) and SKB Gig Rig that plugged into the SoundMachine the next season or two. Also purchased 7 or 8 SM57 mics and cables.
Year 3 or 4 (I forget): Yamaha DTX and snakes
Year 5: Two Yamaha 7200S Amps and a set of Speakers/Amps from Melhart with carts. More than sufficient for our band size and was justified to admin as also being useable for special events like Veterans Day today.
Year 6: Yamaha MOXF88 Synthesizer
Year 7: Battery System from Dan Ryder... Probably wouldn't buy again to be honest. It doesn't have enough power to really power our amps. It works for practices though or if a stadium doesn't have power. Normally we still plug in for power.
Year 8: PreSonus Digital Mixer
If you bought all of our current setup at once you're looking at probably well over $15k. The key I think for everyone is to plan it long term.