Stupid cash-only question (probably the first of many)

My first errand tomorrow will be to go change my weekly payday deposit into cash. I’ll be stuffing my envelopes BEFORE I go do all my weekly shopping. But one thing has already come up – I have a bill to pay this week for my cellphone. In the past, I’ve just transferred the money electronically. How do folks on a cash-only basis handle bills like that? I don’t even get a paper statement with a return envelope. Do folks just go ahead and pay some things like that electronically, or do they actually go get traveler’s checks and mail them off? I feel like a total moron asking this question but I’m not sure what would be considered best practices for stuff like that. Suggestions?