I accidentally stole a basket from the bartender at Riverwood Sleeping Giant Inn, but I gave it back yet he sent hired thugs after me. How do I defend myself without dying even though I'm level 1?
Try turning the difficulty down just for that one fight and change it back to normal afterwards. The game has no trophy on PlayStation or achievements on Steam/Xbox360 relating to finishing the story on X difficulty so you won't be penalised in anyway for doing this.
I had a similar problem where Thugs attacked me as I exited the mine in Dawnstar so I turned the difficulty down by one, killed the thugs and changed it back to the default setting afterwards. On the lowest difficulty you'll take half as much damage and deal 2 times more damage than the default settings.
It is also worth noting that Bethesda probably knew this would be a problem in Skyrim as pretty much every elders scrolls and fallout games have issues where it is possible to be completely stuck because of the games mechanics.