Depends. You already got food covered? If not, where are you from and what's the reason for your trip? It can't be tourist, as you (presumably) won't get a tourist visa for that period.
I'm asking because most companies and educational bodies will provide a means for a subsidized lunch (on average, one meal per workday). I pay ~5 Euros for that subsidized lunch - most other ways of getting something to eat would be more expensive.
Oh, and was was already mentioned, don't bring cash - or at least, don't bring too much cash, 200 € should be ok for starters. Smaller shops (bakeries, butchers) will often be reluctant to accept plastic, or may not take it at all. Otherwise, credit or debit cards (I use Visa and a VPay/CashPool card from my bank) should work, but you'll need a chip-and-pin or wireless card. Speaking of wireless, the Apple or Google systems might also work in some places (haven't tried them yet, it's easier for me to just use my card than having to fiddle around with PINs).
If all else fails, you can use the card to draw cash from an ATM - just be aware that most ATMs will charge a considerable fee for using cards that are not from the operator of that ATM.
Otherwise, it'll depend on what you want to do and where. At my place, a single bus (or train) ticket from my home to my workplace will cost me 3.20 €, an all-day ticket 6.40 €, a yearly ticket 58.23 €/month - but for the latter, I get again a subsidy from my employer, so I end up with spending ~11 €/month for that yearly ticket. Which remonds me - I need to replace the May ticket in my wallet :-)