I carry my change of clothes in a packback - rolled so they don't wrinkle. I keep wipes, deodorant, a brush and a towel at work.
On the hot days I'll actually use a damp paper towel to wipe my face/arms/legs down, comb out my hair and use the towel to dry everything off.
I also drink really cold water when I get in from a hot ride so I can get my core cooled down quicker.