I've used Xanthan gum and some food coloring easier to make and dispose when done using it for some added texture you could also use applesauce as well
4 bottles of mustard, 10 cans of cat food, one jar of mayonaise, 2 gallons of spoiled milk, 1 bag of ferret kibble, 1 tube of ivermectin paste, 4 eye of newt and the spleen of a virgin
Ready made custard + green food colouring makes great green slime. I have gotten some cute guys slimed with green custard and it looks just like the real stuff; but given they typically come in 1L cartons, that means a lot of custard! Have to like vanilla cause it will smell of the stuff!
Also a packet of cornflour + a touch of warm water to turn into liquid + 2/3 bucket worth of boiling hot water which you then add some food colour too after thickening. Makes a good thick gunge/slime that doesn't smell ... this was my go to before gunge was for sale online.
I just buy the stuff online now mostly cause its easier to mix / prepare a bucket worth; and doesn't have any smell.
Edit: just saw you're in the US ... don't think ready custard is available. Do they do large amounts of ready vanilla pudding?
Also, when I say "cornflour" i think in the US that is "corn starch"