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.
How will I survive if I cannot die? I just will
The challenge is in not erasing yourself by the rules, by being famously immortal. Presumably, you also don’t age. So you just have to move around every decade or two.