As far as gestures, accidental pinch-zoom was my worst challenge. It was hard to avoid, and it would trigger my migraines. I understand why small screens need easy scrolling and zooming gestures, it's just I need an option to disable them. Accidental taps were also annoying, of course.
Excessive red can be a problem:
With epilepsy--
https://www.ncbi.nlm.nih.gov/pubmed/10487169
Without--
https://www.ncbi.nlm.nih.gov/pubmed/9163847
Blue-tinted sunglasses can help a bit too.
A lot of styli are designed for a type of grip I can't use. A touchscreen glove should avoid that, but I'm allergic to latex and spandex, and have had trouble with gloves advertised as 100% cotton which turn out to be 2% spandex.