Fortunately, I live where just about anything can be found within 100 miles. I remember reading about some San Francisco-ara people who did the "100 miles" thing for a year. The biggest problems, as I recall, were sugar, wheat, spices, chocolate, and coffee/tea. They finally found some local (and very expensive) flour, but I don't remember what they did for the rest.
Fortunately, there are hundreds of wineries within 100 mile, some of which make brandy, not to mention microbreweries, so I wouldn't have to become a teetotaler. Lots of fruit & veggies year round, but I'd have to eat a bit more seasonally than I currently do, unless I wanted to spend the summer doing a lot of canning & freezing. I'd have to set up a winter herb garden and do without spices and vanilla. Alas, no cranberry sauce for Thanksgiving.
Enough seafood most of the year, including clams, mussels, and oysters. Ocean fish. Crabs, of course. But not much in the way of shrimp and squid is out of the 100 mile range. No problem with dairy, eggs, or meat, but I'd miss some imported cheeses.
All the almonds, walnuts, and pistachios I want, but no macadamias and I'm not sure about hazel nuts.
Plenty of rice, but it would be tough to do without bread & pasta. There used to be a big sugar beet industry here, but it's pretty much gone. There is a cane sugar refinery within 100 miles if I'm willing to also buy stuff produced locally. You can't use honey for everything. Tea would be a serious issue.