Winter can be really cold, i've experienced temperatures about -20 °C and sometimes even more.
Weather can be different from one day to the other, for example one day you can have -18 °C and the day after -1 °C, and specially when the wind blows the temperature you feel can be really way more cold that what it is in reality.
To walk i suggest warm shoes, water resistant, in case it snows a lot or it rains (maybe both at once)
I really suggest a big winter coat with a hoodie, gloves, scarf and something warm to put as layer under your pants
Photo Equipment: Make sure your camera can resist on really cold temperatures, sometimes below -20 °C and keep the batteries always in your pocket, you will save them from a quick discharge due to cold.
Luggage and bags:
Better to have a rucksack with stout handles, since normal suitcases can be very awkward getting on and off transport with
Clothing/Shoes/Weather Gear: Winter Time; Stout waterproof boots are a must, Dress in layers, dont forget longjohns either. Fleeces are ok, but try to get those that zip into waterproof jackets as well. Gloves are a must, as is a scarf and warm hat.
Toiletries and Medical Supplies: always carry toliet roll with you, have a supply of wet wipes for cleaning surfaces and hands with.
Photo Equipment: All equipement pack well, no problems to get films developed and in most cases a lot cheaper than it would cost back home.
Miscellaneous: For summer:Insect repellent is desireable
Warm winter clothers are necessary from October to May, though it can be +3C in January.
Photo Equipment: You wiil certainly need a camera. It may be difficult to find slide films in Petrozavodsk, so buy it in advance.
Camping/Beach/Outdoor Gear: Take bathing suit. Last 2-3 summers water in lakes was incredibly warm.
If you travel in winter you may need it as well to go to Finnish sauna or Russian steam bath (banja).
Miscellaneous: Take repellents to protect from mosquitos, if you go on hiking in summer.