Im in the market for a new sack to carry all my gear in.  It needs to be hold the following kit

thermarest inflatable thingy, Vango Spirit 200+, karrimor lite global traveller sleeping bag, jetboil pcs.

I can fit all this and a few other odds and sods into my karrimor skye 25 litre with a little persuasion, but want more room for luxuries such as food!

I dont really want to go too big as its for wild camping, but I know some bags can be compressed to a lot smaller size when the extra isnt needed!?  I am also more intrested in comfort than super lightweightness as I hate getting a sweaty back with a passion!

Im gonna say a budget of 100 english pund, but I have more if needed but ideally id like to spend a lot less!  I want atleast 45 litres and the idea of one a big one which can be compressed sounds good (save money on buying a bigger pack at a later date) ... what do you suggest! 

The new Haglofs LIM 45 or 55 models are very comfortable with a load but weigh scarcely over a kg each. Retail for under £100 too. See them at Outdoor Warehouse in Windemere. You'll have to decide if you like the features such as the roll-top closure....

If you want to avoid a sweaty back then maybe you need to look at air-gap models? The Osprey Atmos 50 has a lot of devotees (I'm not one of them ).