Let it rain... outside. The rain makes the house more comfortable for me. Bringing lots of horror movies - even cheesy ones because it's fun to laugh at the ridiculousness of such movies. Wearing a comfy sweater - an essential and comfy approved! Chocolates - lots - and any beverage whether it be: hot chocolate, water, tea, milk, or coffee. For me - it be a ton of fun if my best friends were there - obviously. Telling stories (any)/making each other laugh. Playing video games together/by myself (Zelda, anyone?). Finally, sleeping at a comfortable position while hearing the rain or hearing music.
This would be a recipe for a lazy Saturday, but it can be for a sleepover too. Never experienced a sleepover, so if you tried this, then you can tell me if it was great (or not). I love chocolate.