Broad generalities, but for the most part:
1. You can buy anything in Europe that you can buy in North America. Don’t take extra stuff unless you absolutely have to have a specific brand name (like due to allergies).
2. Nothing is cheaper in Europe than it is in US (assuming that’s where you’re from for comparison). Energy costs and taxes are higher in Europe, so most products end up being more expensive. My rule of thumb: double the shelf price at Walmart. Walmart’s price doesn’t include tax, while the price in Europe does include tax, so your actual expenditure won’t be quite twice as much, but that’s what the sticker shock will look like.

I would not try to save money by taking extra toiletries, cooking supplies, etc. You’re spending thousands of dollars to learn/experience the local culture, don’t overpack to save a hundred dollars. Shopping for necessities is the best way to experience the city, learn the language and experience the culture.