I've just made my 3 up a tool box each with pencils, crayons, pens, cellotape ,glue, stapler,scizzors etc. Keeps them quiet for hours.
DD was playing hospitals at pre-school today. They'd lined up chairs and put a doll on each. Had an ELC medical kit.
Playdough definately ,keeps mine quiet for hours. I vary it each time to keep their interest up-glitter one day, my baking tins another, dolls plates, match sticks for making hedgehogs etc
Just also bought my lot the circle palettes from ELC they're fab. Put a blob of each colour in, seem to make less mess somehow.
Library visits definately, bring home the max you're allowed(think it's 8)and keep them in a special basket. Keeps mine quiet for hours.
Foam shapes from Tesco, fold a piece of paper in 4 and sort the shapes out and stick.
Goggly eyes, draw a monster and stick it's eyes on.
Also bought mine all an A4 pad each for special drawings.
Some cheap envelopes, a pile of 1p stamps and a letterbox- they love to write letters.
An etch a sketch-you call out draw me an..... erase then you do one etc.
Old catalogues cut out pics and stick onto a house shape eg beds in a bedroom.
Rolls of paper to draw a road on then play cars with it.
Sticker books
Stencils
ELC has a 20% offer on at the mo and free postage over £40 might be worth stocking up with some craft stuff. Tesco is good and The Works(both cheaper)
When it's the holidays I actually plan out the days and work out a crafty activity and a play activity for each day of the week so I know a couple of things to do each day-keeps us all sane!!!!!!
I've also made a list of all our toys and craft stuff so if they're all fighting I can quickly suggest something to diffuse the mayhem (otherwise my mind goes blank and I can't remember what we've got).
Hope this helps, my twins are 4 and dd just 3 and I remember the 6 month run up to funding, couldn't afford to send them to pre-school before. Keeping things varied really helped.