I own the S,M,and L. The small I pack with all my clothes. Im thinking about getting another small for those 4-7 day trips. However 1-3 day trips the small works great (That being said, take into consideration that I pack light).
The Medium I pack my Stoic 15 degree 650 sleeping bag. Really the Medium is over kill because the bag packs down so small I think I could get it in a small if I tried.
The Large i pack my MSR Mutha Hubba 3Man-3Season tent (poles and stakes included) as seen in the attached pictures.
I highly recommend using these bags for anything that will compress down. Some people have been saying to "roll them up to get the air out". I would disagree with this. I lay everything as flat as possible, place my knee at one end and slowly work all the air towards the air valve. this make your bags long and skinny Vs fat and round like a bowling ball. I then slide all the bags into my pack (BD Infinity 60) parallel to each other. When packed this way it will amaze you how much more run you will get out of your pack.
Using it as a pill works great if you fill it with cloths. Using just air the pillow goes flat in about 15 min (or just long enough for you to fall asleep and wake up made because your pillow is flat).
As far as being waterproof, it is not. Rain, snow, kayaking, things like that it will work great! But dont try and submerge this baby, it wont work. The water gets in where its folded at the top, thats why it works great for rain. Rain doesnt go against gravity. Put this baby under water and the pressure of the water will get in.
.its STOIC, what else do you want. Really though the quality was great. When I first pulled it out I was worried about the valve and welds of the bag. But all that has gone away after using it a few times. The material although durable it will puncher if your not carful. Stoic knew this when they put it on the market and thats why they included a Fix-it-Kit.
All and all
.I use it on every trip
..Buy one (or three)!