Hi reb - I made a full size coffin for a halloween party many years ago out of cardboard and cereal boxes! 2 Large pieces of cardboard cut in to coffin shape, attach cereal boxes all around the edge with sticky tape ( both sides ) & make secure. Either paint the whole thing black or the easy method, cover in bin bags stuck down with sellotape. Buy one of these cardboard jointed skeletons that are on sale to finish the whole thing off! Cover lid the same & attach with sellotape.
I have also made decorations with black crepe paper, you know the kind that you can buy at christmas that stretch and hang from the ceiling. To make these, just cut a width of about 4" off a pack of crepe paper, you can get a few out of one pack, make several cuts in the paper on each opposite side, don't cut all the way through, so in effect you have those Christmas stretchy decorations you can hang from a central light outwards. Buy some cheap plastic spiders from a pound shop, place them on walls ect....
Have you got the ghostbusters movie? The music and film are brilliant entertainment for young and old.
Something else we did for a laugh was having two identical black buckets with a cloth over them. We placed in one, anything that felt like body parts, spaggetti - veins ect... We blindfolded the person and asked them to guess what body parts we had in the bucket. Whilst blindfolded, we swapped the bucket for the other identical one that we had hidden and previously taken the bottom off, when the person put their hand in, we grabbed them!!! EVIL lol!!!!!
You can buy red bulbs for a spooky atmosphere. Hope that helps :0)