light rucksack around 25 liters

Take a look at the ULA Relay. Lots of good feeback on it.

A couple of other good packs in that range are Vaude's Lasona, and the Mountain Hardware Scrambler.

Vaudes new Lasona has and excelent fit and weighs 13 oz. They also have the Ultrahiker that is even smaller(20L).
The MH Scrambler comes in at 11 oz.

No experience with either one other than tring on the Vaude.

Marcin,

Not exactly a brand that pops up on this site very often, but Eagle Creek has a daypack specifically designed for this purpose:

http://www.eaglecreek.com/accessories/travel_necessities/Packable-Daypack-40302/

20 liters, 280 grams, should fit your bill. Great stuff about Eagle Creek is that all there stuff is absolutely bombproof; I've never seen a seam fail on a Eagle Creek bag. And best of all it;s readily available here in Europe.

Unfortunately their site doesn't inform about a dealer in Italy. I do find a store in Geneve (250km from turin: Great Outdoor Store 14 Cours de Rive Geneve, CH-1204 Phone : 0228401757 and Terres d'Aventures 5 rue du Pre Gerome Geneve, 1205 Phone : 0223206729) a bit closer by in Chamonix (170km from turin: Snell Sports 104, Rue Paccard
Chamonix, F-74400 Phone : (33)450530217)

Hope this helps.

Eins

MontBell makes a 21ltr travel pack like the Eagle Creek, but lighter (200grms).
https://www2.montbell.com/america/asp/products/Spg_shosai.asp?cat=1402&hinban=1123200

No dealers of it in Italy unfortunatly, but several stores in Switzerland carry MontBell and they have a dedicated store in Grindelwald. They MIGHT carry this pack.
http://www.montbell.com/english/shop/overseas_stores.html

Thanks, everybody – you're very helpful!
I am now actively looking for a store that would ship one of them to me within a week (I like the mh scrambler most, I think).

BTW: does my english 'sound' italian? I am from Poland, actually :)

No.

"Turin" sounds Italian ;)

http://en.wikipedia.org/wiki/Turin

http://en.wikipedia.org/wiki/Turin_Turambar
Nick goes back to my adolescence times ;)

And Vaude Lasona weights 26oz ! If I fail to buy anything lighter, I'll try to go for Rock Ultralight 25 (14oz).

I use the Rock Ultralight 25 as my all-purpose daypack. It's the only pack I haven't gotten sick of after 6 weeks. It's sturdy too. If I'm carrying heavier, small stuff (so it doesn't look like a sack of potatoes), I put a cut piece from the a ridgerest as a framesheet. It also folds up into it's top lid so can be stored very small.