A lot depends on how serious you are about the sport. I have very large feet, my wife has very small feet so we carry our fins and booties. If you have a very large or small face, prescription lens or any other special needs you might want to carry your own mask as well.
The snorkel is mandatory. For one reason it goes in your mouth.
Two I don't trust the disinfectant the dive operators use.
Thirdly, once you get used a particular size snorkel it is very hard to get use to a different one.
Many dive operators require you to wear a vest while on their boat. If you are not of normal size you may want to consider bringing your own, otherwise I would use the dive operators vest.
Hope this helps.