The provider should have everything you two need. I don't like latex so I use the Skyn brand of condoms. I always have a large box of Skyn ( the ones with extra lube) condoms and a 3 pack of magnum condoms, just in case. I provide my own lube (my favorite), massage oils, and even female condoms.
FYI - The large Skyn and the regular are basically the same size. I had a problem trying to use a large skin on a rather wide dick. I would stick to magnums if you need them.
A good provider will make sure she has everything needed to fulfill your wishes.
You shouldn't have to worry if SuzyQ has another condom for round two or if you wanna take it off for a minute and get some head (female condoms are great for this) there should be another condom in hands reach.
I have had a few guys who need magnums and will bring their own. That's fine with me but I do check the date on the packaging. A lot of the guys I see will leave their favorites with me for next time.