>>1646601If you have good quality kit you can easily fit all the necessities into a 30 L backpack, maybe even smaller. However, that is assuming you do have gucci kit (eg down sleeping bag) and a fair tolerance for maybe being a bit chilly.
More reasonable is a 50-60 L pack, which'd make sense to get anyway for longer trips when you do have a good pack.
Anything larger than 60 L is usually unreasonably large unless you are away for a week.
>Sleeping bagI recommend the Snugpak TSB. £40, used by the British Army, weighs just over a kilogramme, still warm when damp, quite bulky. Probably is a US analogue if you cannot get Snugpak in the US.
>RollmatThis depends entirely on your climate. A rollmat's sole purpose is to insulate you from the ground, and you can potentially use brush for comfort. You could get away with using a common old yoga mat if you are somewhere warmer, but you will need speciality gear if you are somewhere quite cold.
>MedicalPlasters, burn dressings (I recommend simple burn gel sachets and then put a plaster over), alcohol-based hand sanitiser, allergy pills, space blanket, ibuprofen and paracetamol (or whatever you call them in the US), and a mobile phone with a charged battery on a low-power setting.
>CooksetHighly recommend the Trangia 27-UL. Check eBay, use common methylated spirits as fuel. If the Tranny burner gets too cold to light (or even unscrew) what I do is screw the lid on, daub some hand sanitiser around the rim, set it on fire and leave it to burn out. This'll make the metal swell so you can unscrew it and will prime the meths so you can cook.
>FoodGet a ratpack/MRE if you fancy. 3,000+ calories prepackaged for reasonably cheap. Nescafe original/strong individual sachets are very tasty and sugary if you need a quick hit of energy/warmth. 3 litres of water; 2 for drinking, 1 for cooking.
>KnoifeMora.
That's what I do, and what I'd recommend to a new beginner.