For cases where it's worth it to you to pay ~2.5% (to hit your spending thresholds, or because you're getting a rebate on gift cards, etc.):

http://www.flyertalk.com/forum/miles...-taxes-cc.html
(You may also want to look into pros and cons of overpaying your taxes just before you file.)

http://www.flyertalk.com/forum/other...smart-com.html
(For a utility bills, car payments, mortgages, etc., but only from certain companies.)

http://www.flyertalk.com/forum/miles...nt-online.html
(In your case, maybe you can pay your friends' rent.)

Do buy a small amount of coins ($250, or $500 if you want faster shipping) to cover your personal spending that you do in cash.

That should be all you need to get nearly 100% of your spending flowing through your credit cards.

Finally, one warning: my impression from reading various threads here, on fatwallet and elsewhere is that spending close to or more than you stated income on credit cards from any one issuer sometimes triggers financial review or other not always warranted adverse actions.