Having climbed most of the munros that are easily do-able in a day, I’m now looking for a bag that will take a few days food and gear. I’ve only owned 25-35 litre bags.
If anyone has any pertinent info, it would be greatly appreciated.

My advice is to take all the gear you are planning to be using to a shop like Tiso and ask to try out some bags. They won’t mind and it is the best way to see what bags your gear fits in. Try as many on for fit as possible as they will vary a lot between models and sizes.

Once all your gear is loaded up, you might decide you have too much stuff and would prefer to go more lightweight. Again leave out non essentials and try loading up some smaller bags to see the difference.

Have a look on http://www.walkhighlands.co.uk/news/gear-review-rucksacks-for-wild-camping/008349/ for reviews and also Chris Townsend covers backpacking gear lists in some youtube vids and on his blog if you have a search for them.

I use a 45 litre bag for summer camping when doing munros. I find this gives me enough space for a night or two and doubles up as my winter day bag as well. I like to keep things simple though and only take the essentials. If I wanted a bit more home comforts then I would be looking at 50 to 65 litre bags but then it is easy and all to tempting to overdo it and end up lugging a monster weight up and down the hills which I don’t enjoy.

I have a couple of Osprey packs and would highly recommend them, very good build quality

I’d say Osprey and choose a size that fits best. They’re so light that I’d to for a big one.

black diamond
Osprey
Macpac

personally something in 40 to 50 ltr range

one that keeps going for me is a Lowe Alpine not sure what they are like today

own all of the above makes

I love my Podsac. Seems really well thought out. Well made, and well,spotty dog IMHO.

Podsac

I have a lightwave 60l and a Gregory 40l for DoE duties. The Gregory is about 33% heavier for less volume,but is comfier. As said above try them on loaded. Oh and email in profile if you want the lightwave. (M/L size, 1200g)

Go large and be disciplined when you pack. It’s a ball-ache having stuff on the outside of a too-small pack. Plus a bigger pack is good for anything, including winter when you’ll need more kit. Mine’s a Lowe Alpine Appalachian – it’s pretty good, though not the lightest. Mate has a Pod and he rates it.

Going large usually means you’ll fill it with stuff you don’t need

My go to 2/3 day pack is a Golite Jam, but it’s a frameless pack so unless you’re confident with using and packing it I probably wouldn’t recommend it

Osprey is a good shout, something around 50 litres should be enough, though more days usually means more food, not more stuff. 70 litres is way too much unless you’ve got quite basic bulky kit, will be heavy once that’s packed too