We used to do the putting your hand in a bowl to guess what's in it thing... Tell a story - my Mum always went for 'I was on my way here, I stopped at a shop, then when I came out there had been a car accident. I stopped to help but I think some of the body parts might have got in with my shopping...'
Put food stuff in bowls and cover with a tea towel, get them to feel and guess what it is (can be done without the story for more sensitive souls). Good ones are baked beans, dried spaghetti, mushy peas, orange segments, kidney beans etc.
Could they make their own pizzas for tea? Either make the bases from scratch, from a base mix or buy them ready made and just add toppings (depends how adventurous you feel).
T-shirt painting could be good - cheap t-shirts from somewhere like Tescos, then you can often get cheap t-shirt pens/paint from places like The Works or Poundland.
Big bowl of dried peas, give them a smaller bowl/cup and a straw each and give them a minute to see how many peas they can get in their small bowl using only the straws.
Ring donuts dangled on string and they have to eat it without using their hands.
Rent a DVD, make a big bowl of popcorn, turn all the lights off and watch it under quilts/sleeping bags.
HTH!