How nice of you to think of that for your friend! I wish I had a personal attendant at my wedding...I did during the reception but during the actual ceremony, no.
From my experience: I say of course makeup for touchups (mascara, eyeliner, gloss or lipstick, foundation, oilblotting papers, evian spray to freshen up the face, baby wipes to quickly remove makeup, basically the whole kit to redo the face if needed), hairpins and comb/brush to freshen up hair, hairspray, perfume, breathmints, those little toothbrush things they make now for quick freshen ups, antiperspirant that is clean and leaves no streaks, small towels for freshening up, pantiliners, (if she is wearing hose) replacement hose, a second nice comfy pair of shoes, stain remover pens, white chalk (if the stain can't come off and you are desperate, at least you can cover it temporarily and the dress can be dry cleaned later). What else? A camera to capture everything! That is all I can think of.
I should also mention a small sewing kit.