Get creative with your baggage allowance. You're allowed a carry on and a personal bag, so use them. Are you allowed one free checked bag or two with your airline? How much weight are you allowed? Is sporting equipment (scuba gear) allowed free? Check. Those might influence your decision.
Use fin pockets, etc. for small items. Roll your clothes instead of folding them to squeeze the air out, take less space, as well as keep them less wrinkled. Think about clothing/accessories you may not really need. Pack for the typical weather possibilities. Lighter clothing is preferable.
I prefer to take all my own gear and normally do, (except tanks and weights, of course). I know their maintenance history. Once when really pressed for weight/space, I took just my personal gear: wetsuit, mask, fins (since I have tiny hard-to-fit feet), light, and SMB. Check with the shop you plan to use if they carry the type of rental equipment you want, if you're specific or hard to fit.
Good luck and have fun!