Three-week Central Europe on a budget this fall: cheap eats, rail passes.

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I'm planning a three-week backpacking trip through Central Europe this fall, aiming to keep costs low without sacrificing the experience of smaller cities and local culture. I'm comfortable with hostels and public transport, but I'm looking for specific strategies beyond the obvious. For seasoned budget travelers, what are your best tips for finding affordable regional food, leveraging rail passes effectively, and discovering free or low-cost cultural activities in cities like Prague, Budapest, and Krakow that most tourists overlook?