Its pretty much a choice between cost and if you would use it later. Some folks buy (and bring) their own mask. Its great to have one that fits perfectly. The dive shops have a good selection, and most folks rent them and do just fine, but if you plan on using it at all later go ahead and get one. Fins take up more room in the luggage. I'd probably rent those.
If you decide to buy one, stop at a scuba shop and let them help you. Each brand and model fits differently, so you'll need to test them. To test them, hold them to your face with the strap out of the way. if you can hold it to your face just by inhaling thru your nose, it should be watertight for you.
To check if the mask fit, put it against your face (don't use the strap) and take a deep breath. If it stay on your face then most likely it's a good fit. Then after you buy it, put a thin layer of tooth paste (on the glass) and rinse it off, Otherwise it will fog a lot.
Make sure you 'rub' it into the glass. Do this at least a half dozen times with a brand new mask. The manufacturers spray them with a protective coating (the lenses). This coating will cause rapid fogging unless removed. Toothpaste (most kinds, especially the old fashioned 'paste' rather than gel) contains abrasive material that will gentle scrub off this coating. I've also known people who have had good luck with the product Soft Scrub, a kitchen cleanser. Any mild abrasive will work.
If you are planning to dive in the future, buy the mask from a dive store.
You don't need to spend a lot of money to get a good mask. Try these two:
Tusa Liberator (have friends that swear by it)
Sherwood Magnum 2 (I have two of these, best mask I ever owned) I've paid more for the others but don't use them.
You don't need an expensive snorkel either. Some people like the dry and/or purge ones but I like a simple large bore snorkel with a flex. Trend in the industry lately is to add a 'new' gizmo to snorkles every model that comes out it seems. Dry, water funnels, flappers, purges, ect., ect..... much of these are simply what you get used to and are comfortable with. There isn't anything wrong with an inexpensive standard open tube snorkel. Nothing wrong with one with gizmos either...except that the more bells and whistles, the more to break or malfunction (my opinion). Again, get one that is comfortable in your mouth, and that the tube isn't over-large in diameter or lenght (creating dead airspaces leading to CO2 buildup). Most standard brands will have an acceptable size tube.
Snorkel masks don't have to be tempered glass like scuba, tho most are depending on pricepoint). Key thing as mentioned above is fit. If it fits and seals well, and is comfortable, it's the one you want. I've found $25 masks that will work WAY better than a $100 mask, becuase it fits a face. I don't even look at the price, and advise folks the same when mask shopping. Try them all for fit, find the best one, and then look at price.
Again as mentioned above, best way barring the pool or 'toilet test' is to place the strap in front of the mask, slightly press the mask to your face, and inhale to create negative pressure inside the mask. Then hold your breath (do NOT continue to inhale), lean forward, and see if the mask comes free from your face. A proper fitting mask should hold the seal.