Supposing you abruptly time-traveled to a past era, and when you arrived you had none of your current 21st century possessions with you. How far back in time could you get by reasonably okay, given what you know now?
In the era you selected, what would be the thing 21st-century you would find the most difficult to do without?
What would you NOT miss?
Do you have any skills that would be useful during that previous era?