Here's what I did, and why:
1) Before I was certified:
--- Mask, snorkel, fins, gloves, and wetsuit booties, because I had them from previous snorkeling trips (although oftentimes you might choose different fins later, and/or for diving; so if I did not already own fins I might try to rent/borrow until a bit later).
2) On my first dive trip:
--- 3mm wetsuit, because I'm hard to fit, the rental suit was not too great, and there was a new suit at the shop there that fit me.
3) Before my second drive trip:
---BC, because rentals never fit me and were always different from dive-to-dive (this changed diving for me completely -- fantastic!)
--- Regs, because I figured out that between the BC and the regs, the rental fee would have been nearly the same as buying a good set of used regs (my buddy bought an on-sale new set at the same time for the same reason). I never had any real problem with rental regs, but.... I never liked the "ewww" factor of them (communal mouthpiece).
--- SPG
--- Computer (was a gift when buddy upgraded to an air-integrated computer
)
4) During that trip:
--- Compass (because we were going to take Navigation as part of AOW, and because it was not good to have to rely on my buddy's.
--- Reg hoses, because I wanted to try different lengths.
--- Better gloves (cable leading down to wreck is encrusted; plus I just like to wear gloves).
5) Before the third trip:
--- 5mm wetsuit, because it was a good deal on Craigslist, and because I was anticipating chillier water in winter (even in Florida).
6) During that trip:
--- Hood (brrr....)
7) Before trip #4:
--- Weight belt, because I got tired of the rigamarole of figuring out which one would fit in the morning at the dive shop before heading out on a dive, and/or ending up with one that was so small I could barely get it fastened, or, conversely, a mile and a half of extra belt flapping away. Also, the plastic buckles on most of them made me nervous.
--- Four 1# weights (because the boats I've been on either don't carry or quickly run out of this size; if I need more/larger weights, I use them from the boat's supply).
7) On my list:
--- Tank(s) (Not necessarily worth the expense/hassle right now for the type of boat diving I have been doing, but I would like to get steel tank(s) for possible shore diving/other places; and I really wish I had a tiny tank (Jax, I need that AL3!) to attach my regs to for soaking.
--- Drysuit/warmer wetsuit (Then I could try diving in new places!)
Note: #7 is not all-inclusive
Blue Sparkle