I often tell new divers who are contemplating their first dive equipment purchase to consider what often doesn't come with rental kit. The first items that come to mind are often the ones most needed if you get into a jam on a dive. Most often rental kit doesn't come with a SMB/safety sausage, whistle/noise making device, cutting device, or light. You can often purchase these with a low investment cost, clip them to your rental kit and have them available while you determine what set up is best for you. They also pack small so traveling with them in addition to mask/fins/snorkel/exposure suit is rather simple. Just a little food for thought.