We took the Epi pen with us to the pool and left it in our beach bag. You never know if or where someone's little fingers leave peanut butter smears. The room safe is just too far. The resort pools had those little lockers available, but we feel safer with the epi pen close by and handy. You can have your credit card loaded to your magic band so no need to take that to the pool. As far as having your id you would really only need it for adult beverages. Try and put the id in a ziplock bag and then into a pocket of your bathing suit. Ladies, make him wear pockets.
I bought a waterproof neck pouch for a water park trip. Not high fashion, but it worked. Read loads of reviews and found a decent one for $10. Bonus at the local water park was skipping bag check since it was see-through. Big enough for a phone or epipen, but not both.
I'm sure I could look this up, but is it safe to assume MB is waterproof?