Mirroring what KenK said, after our fall Cub camp near the end of October (it dipped down somewhere between -5 C & -10 C) I was reminded that I really should've brought my bum pad along ... it would've made sitting around the campfire much more comfortable. I wear my Cub blanket poncho-style so it doesn't do much for insulation down there:).

There are commercial ones avialble (like this), but I just cut up an old blue foamie that wasn't in use to make a couple for myself & the kids.