Megatron, I'd suggest one of two courses.
If you're looking for a generic day-to-day bag then I'd pop into a local outdoor shop, try on various packs between 15 and 25 litres, and see what you like. I think that they're much of a muchness.
Alternatively, if you want something more special then I'd take a look at what's in the sale at Oki-ni
(I particularly liked the White Mountaineering
, Silent by Damir Doma
and purple Masterpiece
, End Clothing
(the WTAPS backpack
isn't in the sale, is lovely, but expensive), and Bill Amberg
I was in Liberty's of London a week ago, and they had an otter green Filson rucksack
and a Jas MB leather daypack (similar to the White Mountaineering design).
The other thing that I'd be considering would be saving up for one of the leather satchels that Margaret Howell
(not on the website) or the Merchant Fox
(made by Tanner Bates
, and it'd be cheaper to go to source
), which would likely last a lifetime or two. They're not cheap though.