The weather in Tomsk in summer can change very quickly from hot sun to drenching rain. A strong umbrella or lightweight waterproof jacket is essential.
Toiletries and Medical Supplies: Insect repellent to deal with the midges is helpful. I put it on my arms, neck and face, but forgot to put it on my legs, and got bitten there several times.
Miscellaneous: I travelled with the Lonely Planet Russia guide book (not the Transsiberian one). On the photo you see the new edition but of course I travelled with the older one and I didn't carry the whole book but ripped out the necessary pages. My travel mate had the Transsiberian one from Trailfinders which is really good.