Regretfully the Rab Neutrino bag I took with us (albeit 3 years ago now - how time flies) did not last more than a month. Lovely bag, but had some big issues and one of them was the thinness of the material itself which meant I ended up having to stitch it back together several times in that single month due to minor 'issues' resulting in holes that the down came out of. I have other Rab bags and they have been stunning, just not this one. I may have ended up with a duff bag, I don't know, but repeatedly having to repair the bag before I could use it got to be frustrating to say the least.
Laptop - entirely up to you, but my OH is heavy handed and we took a Dell Latitude E4310 with us which is a 13 inch screen. We put in inside an
Exped dry crush bag designed for laptops, and my OH carried it vertically in his rear pannier against the pannier rack. Several times the bike fell over onto it and it was never an issue - I am typing on this on it now as we speak. We did buy the world wide insurance with it (complete care - only covers around half the countries in the world though!) to cover any potential issues such as hdd failures and broken screens etc (I worked in a school as an IT Engineer) and saw way too many broken screens from laptops being dropped/knocked etc not to take something because I though cycling with one would be a problem, but I was very pleasantly surprised as to how robust this machine actually has been.
Dynamo hubs work, so do solar panels to recharge AA batteries. We also have a power gorilla which we found to be much more useful - which recharged from a solar panel or mains (either will do) and I would guess if I really wanted it to, it would recharge from the SON28 hubs we had, but I never bodged together a connector for that.
Get your Russian visa before you leave the UK... Ukraine at the moment I would be tempted to give a miss, but be aware that if you do go there, like a number of other eastern European countries, there are limited border crossings that you can use and they are pretty much all the major roads rather than those minor roads we all much prefer. Just pretend to be a car and get on with it... We had fun crossing into Belarus because of the issues relating to a bike not having a registration plate, in the end we became Bike 1 and Bike 2 (at least that is what it translated to!)... You may have to cadge a lift to get across the border crossing into Ukraine from Poland - that is one I have often heard about having issues with, but usually someone with a van will help out and take you 1-2km including the crossing - its a bikes not allowed problem...
Water - depends on how much you value your health! you will need more than 1 method unless you go for the newer less tried technology. We took 2 methods, a katadyn water filter which took out bacteria and protozoa (plus larger matter) and then a UV pen for killing viruses. The UV pen took specialist rechargeable batteries which we could recharge with mains or that
PowerGorilla of ours.
If you have time, consider taking a suitable first aid course for remote areas. Something like this I can seriously recommend. Not cheap, but then being able to save your own life when you need to (or someone else's) is worth every penny in my book (and we ended up needing to save my life when we were attacked by a pack of wild dogs and I was left with a severed major artery, severed nerve, punctured major vein and needing +100 stitches to a very serious leg wound and a husband in shock - he had also been bitten in temperatures below -15C.).
http://wildernessmedicaltraining.co.uk/explorer-series-far-from-help are an excellent company and well worth the money.
Edit: we both did their 4 day course which is exceptionally useful!
http://wildernessmedicaltraining.co.uk/advanced-medicine-4