Stipulations:
- You cannot die and are immune to disease
- You cannot alter the future such that you change the world from your point of origin. i.e. You cannot become so famous that future people recognize you as immortal.
- If you vary the timeline too much you will cease to exist.
It worked for our ancestors for hundreds of thousands of years. Wake up, chase antelope until it dies, spend the rest of the day hanging out by the fire and maybe doing some fishing. Gonna get real good at cave paintings, honestly sounds pretty fucking good.