Looking for some great things to toss all over my bed then my girlfriend and I will sleep a night in the mess!

That's a great idea! I'm so jealous! I have always wanted to do that with my wife! What about some caulking or paint?

Fabulous idea. I second paint. Or something super sticky like marshmallow fluff

Start with something easy to clean, like whip cream. Then slowly get messy with progressively worse thinks. Obviously include shoe filling and accessories, phones, wallets, maybe even a purse.

I like the more slippery things for bed wam, like gunge/slime (natrosol, hec, methylcellulose, xanthan gum etc)

I'd avoid food items if sleeping in it all night because your body heat might make it go off.

If it dries in your hair overnight, just get your hair slightly wet in the morning, apply conditioner and put a shower cap on and go and do something else for half an hour or so, then it should wash out just fine (even if it dried rock solid)

If your sleeping in the mess- avoid dairy based stuff as it'll put up a right stink after a few hours. Same for anything in the fridge.

Likewise acidic foods (ketchup- containing vinegar) or alkaline products such as shaving foam are likely to irritate skin and dry out hair.

Slube is an amazing slime to play in- stretchy stringy slippery it feels amazing to play in with a partner and/or just slide around in. I used a single pack with about 8-10 liters of warm water, making a thick stringy lube. It's a full on sex lube too- if things get steamy you can carry on and slide right into it. The downside of Slube is it tastes of soap and doesn't mix as well with other gunges/slimes
(Slime-Baff is a near identical product in terms of ingredients, just marketed as a kids toy)

Regular gunge such as Xanthan gum/natrosol/MS gunge is fantastic too- its all PH neutral/skin and fuck friendly, and designed to be non-staining. Overnight will probably destroy your bedsheets and require a longer shower but won't leave your skin bright red/purple like food items/colouring.
Clay and MS 'Clayzee Colours' are pretty fun too.

If you want a little texture- try Gelli-Baff (small-medium lumps), MS Jeli-Mix (large chunks), porridge oats (small lumps), or MS VIVI/VIVI extreme slime (stretchy/super stretchy)