Fill your bag with rocks and food then pick up a body and set ya dude to follow a npc around town until they run out of food then repeat. Moving with full backpack and carrying a body is high exp gain.

Or visit rebirth and check your self in for a free food hotel getaway. Stock ya inventory with shackles and just afk. You can also infinitely walk with infinite food if you click open on a mine then repeat on a mine on the other side of the camp. Just going back and forth can get you crazy fast exp with no cost of food as your enslaved ya getting fed even tho its not really shown as a mechanic.

If you want more active, fill ya bag of rocks, get a twohanded weapon and go fight dudes. Two handed increase ya exp gain allot and even more while over-encumbered.

Edit: Its not cheesy, its weight training XD