There are two ways to do this without sacrificing sterility: You can turn the cooler sideways, cover the inside and the opening with saran wrap, and cut two holes in the saran wrap over the opening to make a sterile work box.
(You; cut; two holes; to make a sterile work box) (You; can turn; the cooler sideways) (You; cover; the inside and the opening with saran wrap)
You You You
cut can turn cover
two holes to make a sterile work box
the cooler sideways
the inside and the opening with saran wrap