I would say to NEVER MAKE AN ASSUMPTION THAT SOMETHING IS AVAILABLE FOR RENT. Same for ammo. Never assume these things will be available at the field unless a game host states it specifically in the game announcement.
If there's a game you want to attend, contact the organizer and ask if they have rental guns / goggles / whatever. Most venues DO NOT have guns available for rent. Gun rentals are usually privately handled by players who have a couple of extra "loaners" that they can rent out at games. It's not like paintball where you can rent everything from the field owner.
At the very least, you'll be expected to show up with a suitable BDU, boots and your own food and water for the day. It's usually a good idea to show up with your own ammo as well unless you know for sure there will be some available on site.