Solution One: Put a smaller freewheel cog and a larger fixed cog on your flip/flop hub. Use freewheel for longer/hilllier/fitness rides so you can mashu up and coast down. Use the fixed gear when in town/short rides. Carry a 15mm wrench.

Solution Two: Get a geared bike.

Crank: Has it been overtightened? If so, buy a new bottom bracket.

Chainring-bolts: Make sure they are greased. Ungreased Chairing-bolts come loose easily under strain. Get a proper chainring-bolt tool for a few bucks and use it once in a while.