I equate renting a snorkel with using someone else's tooth brush. Combine that with playing with a rental mask in the water for half your snorkeling time trying to get a nice water proof and comfortable fit and you end up with the buy your own decision.
Not necessary to spend a lot of money on a mask and snorkel. Brands like Body Glove
are decent quality eqipment for the recreational snorkeler and cost about $20
for mask and snorkel at warehouse type stores and mass market department and sporting goods stores. Same brand (and others) also make comfortable and light weight fins that sell for about the same price. An inflatable snorkel vest is about $30 to $40 and you might have to go to a dive shop or a "real" sporting goods store for that.
Always the internet.
If you wear glasses and are nearsighted invest about $100 total and get corrective lens put in the mask. What a world of difference this makes underwater!! That can be done at any dive shop.