You never see time travelers use salt in get-rich schemes, but for a few bucks at the supermarket you can have salt of quality and quantity rarely seen in the ancient world. Show up to feasts and just hand the salt around. Make it rain salt. You'd be able to get plenty of shiny rocks for that.

But no, time travelers always bring gold. Never salt. Despite the fact that "salary" literally comes from the Roman word for salt.

Basically, go back in time, bring salt, exchange salt for worthless trinkets, return to future, make a killing on the antiquities market.

For that matter, show up with some stainless steel. Or what about aluminum? The ancient world would go apeshit over aluminum.

And that's saying nothing of going back in time and being a wizard because you remember a little calculus from high school. Hell, the concept of zero and Arabic numerals would blow their minds when used at the right time.

What about going back in time and bringing refined sugar? You could print your own money.

But no, they always do the boring thing.