a Mountain Bike;
a “Seed” Potatoe [unless I’m being dumped in South America],
& a Farmer’s Almanac
The Farmer’s Almanacs are all done specifically for the year in which they are published, as well as being specific to a geographic location. Not helpful for the 8th century AD.
I’d imagine such a time traveling person would be viewed with suspicion so a weapon or personal protection should be one of the three. I’d go for kevlar body armor, discrete, could be worn under period clothing to blend in. As big a box of antibiotics as permissible would be another, those were plague years. For the last, I’d go for a set of DIY books with a survivalist bent, like the Foxfire series.
Then, I’d have to swallow my American distaste for such things and engratiate myself to the local lord as quickly as possible, lol.