I live in Europe and what i feel most expensive is travel and food here,so it would be cool to purchase items from supermarket rather than at station or outside from the normal stores in the market.Prefer taking day pass rather than point to point tickets
For stay- use hostels or bnb
Airtickets- book well in advance
Food- cook at bnb or carry packed food
Commute- rent a car or use city cards which includes all modes of transportation.