Food & Water is an area you must be careful in, if you are not eating at good hotels. Hepatitis "A" shots are a good insurance for your health. Russia does not have the same controls over food quality as we have here in North America. If you are buying from a street vendor and something looks interesting & tasty, don't be afraid to have a good look at what they are serving. Russians have many different deep fried foods that they sell on the street, have a look at the oil they fry it in. If it is black don't buy it. Your stomach will thank you for it. If purchasing food in a market or food store, check the expiration date on the product. It is very common to purchase jarred or sealed food products that have long since expired. There is no control over the selling of expired food products. It is buyer beware. Russian vendors will try to tell you that it is the packaging date not the expiration date. Don't believe it. I should also point out that Russians sell fish (fresh & dried) with the intestines included. Russians eat the whole fish, intestines and all, something to remember when having a bowl of fish soup.
Only drink bottled water in Russia, it is well known that Russian water is contaminated with PCBs, Nuclear waste and all other sorts of chemicals. Bottled water is available in most areas now, you just have to look harder in some places. Try to purchase Finnish water or Bulgarian. Some Russian or Ukraine bottled water is okay but you never really know, it can be the same water that comes out of the tap. You can also purchase Mineral water, just don't buy the Russian Mineral water, it is not very good.
Russians love Ice Cream and it can be purchased just about on every street corner no matter what time of year. Most Russian ice cream is good.
Russia now has normal food stores with buggies and cashiers, with a good selection of food to choose from. Russia now also has many nice cafes to have a bite to eat and prices are reasonable, even cheap in comparison to our prices and food is good usually.