I would like to go back to 11.Aug.1999 which was the day of the last total eclipse in the UK. I was in the correct place (Devon/Cornwall) for the totality path but it was cloudy where I was so wasn't much to see except it going pitch black for 90 seconds - 2 minutes. I would use the historic weather data available to locate one of the few sunny spots and obviously would use my Samsung S23 Ultra (high tech stuff in 1999!) to film it.
1999 was also the year that I got online, so would be nice to take a gander at some Web 1.0 pages on slow 56k dial-up. Then of course I'd play out Hampsterdance the way it was meant to before anyone have heard of the term "internet meme".
2nd choice would be NYE in the same year 31.Dec.1999, but NOT at my parents this time. I'm still reeling now that I was billy-no-mates and having to stop in on that NYE because my mate down the road had spontaneously arranged something else that day with another group. I'm a guy that likes pubbing, clubbing and house parties, not stuck in at home in 1999 and now in 2023!