Being a commoner in a D&D would be like being a New Yorker in the Marvel movies - constantly living in fear of being sucked up into some supervillain's plot, or, worse, having your life and livelihood destroyed as part of massive collateral damage caused by the "heroes.'"
PCs don't go to the bathroom, there is no game mechanic to cover it. Same with needing to eat more than once per day or having to shower. You can live a poor lifestyle and be as healthy as a noble.
Think of all the cool ideas you can bring to the fantasy world and dominate it. All the threads we had on wreaking the economy with continual torches and arrows. You can create guns and bullets or modernize the medical world. If you went there, there are all sorts of processes that can be incorporated. You could revolutionize labor like Henry Ford and crank out mass-produced wagons for cheap.