I carry one of those little 1-time foil packs in any of my camping/hiking adventures and when on the motorcycles. It's not for use while I camp, it's kept there for that time I come across someone borderline hypothermic, the guy with that compound fracture from the accident (to prevent shock/keep bugs and debris out of the wounds), and that sort of thing. To be honest, a plastic garbage bag does the same thing a lot cheaper and probably lighter. The difference is that the bright silver can be used to attract attention.

If you are looking for a bit of extra warmth the Thermarest liners have a pretty darned good reputation at very reasonable prices and are meant to be used regularly. They also keep the inside of your sleeping bag a bit cleaner.

I can't say what the range on the little alcohol stoves are as I use the little screw-in types for the MSR Pocket Rocket. Those have been down to 14 degrees with no problem (probably less). It's not uncommon for us to wake up in the middle of a frigid crisp night, throw the little pot on for hot chocolate while start gazing. The colder the night, the clearer the skies tend to be.

I haven't tried any of the liquid fuel burners yet.