The best thing I've found is putting together a toolbox of ideas to deal with illnesses. None of my son's illnesses in daycare, as far as I know, were vaccine-available ones, but the toolbox was incredibly useful for preventing those illnesses from turning into anything serious, and to make them manageable. He got sick a lot (we've got some health things going on) but, for example, we weren't up all night sitting in a steamy bathroom, and he didn't have problems nursing due to a stuffy nose.
For us, nutritional supplementation has been the biggest help, but I'd read old posts on illnesses (Momtezuma Tuatara's old posts are a treasure trove of information), read about gut flora, lurk in Health & Healing.
For us, it made the difference between a sick kid who heals with support at home, vs a kid who would've been a regular at the pediatrician's office.