My DD loves her easel with a blackbord on it for chalking. Baking is a hit-your mistake was to only let her do the decorating bit. Put aprons on and be prepared to wipe down the entire kitchen afterwards though
Bread is also good, kneading can take ages if you let it.
Making sandwiches is good, lay out slices of bread, blunt knives, sauces, sliced ham, cheese, tomatoes, etc.
Planting veg seeds is good, then she can watch her veg grow and the cook and eat it. Use a mixture of seeds, so some things are ready quickly (salad leaves are good, or even good old cress) and some take a bit longer.
DD1 was formula fed, so we kept some of those tins with the lids, which made brilliant drums and shakers. Same for old bottles (with the flat cap bit instead of the teat). Just fill with dry lentils, beans or rice, sellotape the lid on and stick stickers and colourful paper all over.
My Dad did a good one-he got a big bit of wallpaper and they decorated it with various pictures of fish, coloured it blue and put it behind the fishtank as a backdrop.
We made worms the other day- mix up some brown paint with pva glue and coat some bit of wool (very messy and so a great hit) then stick on paper.
My tips for minimal messing about are long sleeved apron thingies (elc so a great one with a snail on the front) and, if you have space, "doodle drawers", ie we have a small chest of drawers (I think it is meant for filing paper) and each drawer has a different thing, so we just take out the drawer we need and sweep everything back in when we are finished. We also have a corner with an old coffee table which is just the right height for her to sit at.
Brill places to get stuff are the surestart centre (ours have a cheap craft shop) and the discount book shops. Grown up craft shops tend to be too expensive. Also, keep hold of colourful sweetie wrappers, buttons, scraps, etc.
(and watch Mr Maker :D )