On the subject of filters and mono film, I think I've read somewhere that filters affect Ilford XP more than other films.
This week I bought:
1) A 20mm push in B+W yellow filter from Australia, which I ordered before I found out that 20mm is a tidgy bit too small.
2) Yet another second-hand 52mm Hoya HMC sky1B filter, which, yet again, has turned out to be a bit too damaged to use.
3) One of those "X-tra large camera backpack" thingies, which are sometimes branded "Unho" and sometimes unbranded. Mine is unbranded. The waist belt isn't very good and due to where it attaches to the body, I can't fold it back around the bag to get it out of the way. If I have the shoulder straps as tight as I normally have them on my normal backpack, the "waistbelt" is an "above the belly button belt" lol. If I loosen the straps so the bag sits lower and the waistbelt actually becomes (fairly near) a waistbelt, then the strap across the chest almost strangles me, lol. luckily I don't use chest straps. Anyway, with the shoulder straps and waist strap adjusted so some of the weight is near my hips and then the shoulder straps tightened, it seems quite comfortable. The lower section is just large enough for various kits I have, eg camera +24, 35, 50 and 105mm, or 24mm and 35-135mm or camera and 80-210mm. The upper compartment fits in butty and biscuit boxes, first aid kit and emergency stove and fire-lighting kit. There is a removable padding thingy between the shells of the upper compartment which could slightly increase the space in the upper compartment. There are fewer pockets on this bag than there are on the £100+ Tarion and that other one (whose name I can't remember), but for half the price (and probably slightly less storage space), it seems to be reasonable.