Several pairs of really good jeans, whatever your figure you can get them to flatter you/cover bits whatever you need them to do.
Strappy tops - a ton, in different colours. I have a few nice ones by Red Herring Debenhams, little lace, fit well, like £8 or something each,
Several nice cardigans to wear over strappy top - one black, one another colour.
Nice pair of knee high boots, nice pair of shoes.
Almost Make-up by clinique - this is fab, its basically tinted moisturiser, so if you do not have time to put loads on, this freshens your face
Mascara - normal everyday wear/senstive one, wont hurt your eyes too much, esp wth contacts.
Lip gloss - slightly tinted/clear.
Short nails / clear nail varnish.
Couple of nice peices of costume jewelry to wear (beads, crystals, that kind of thing), same with rings, couple nice bands, alternate to add some glam.
Brush your hair - use a good conditioner if you get knotted hair. Leave it on for 30 mins once a week.
Carry brush, foundation/tinted moisturise, lip gloss and hairbrush in bag, quick once over when you are in loos, just about to get out of car.
This will give you a base, then you can buy/add things as you see them, have time to dress up more.