The way i gear up / know what i need goes like this, in this order.
Torch (Not necessary but useful for dark caves)
Weightbelt and Weights
Knife (on forearm / bicep)
Mask and Snorkel
Float with Blue and white dive flag
If you have all those (some are not necessary i.e. torch, two piece wetsuit etc), then you are good to go. Most important thing to have is a float and flag to indicate there is a diver in the water, which will avoid accidents involving yourself and a speeding jet-skier.
Full time cameraman, videographer, boatie, flasher holder.