I use a lot of
#6 countersunk, and (mostly) #8 countersunk, a few pan heads, of both sizes, some tinnerman (CS) washers. Usually half-inch and three-fourths lengths will do for everything. I buy my assortments through Hare aviation, in Texas. For everything outside, I use stainless Phillips head, but there are pros and cons (of course) on these.
Ron