What should I pack for the last week of August in the UK?

What should I pack for my trip to the UK during the last week of August?
Edit: Thanks so much for all the helpful tips! It looks like our trip is turning out a bit different from what we initially planned, so I’ve created a new post for anyone who wants to assist us in better organizing our itinerary. You can find it here:
https://www.reddit.com/r/uktravel/comments/1j9nt9s/help_plan_our_uk_trip/
I’m an American traveling to the UK for the first time to attend a friend’s wedding, and I’m unsure about what to pack! While I’ve come across a lot of advice saying to “expect all types of weather and pack layers,” I’m looking for something a bit more specific as an over-planner. I’d also really appreciate a link to an outlet converter—I keep seeing different options online and I’m unsure which one to get.
We’ll be flying into London and then heading to Cardiff, Warwick, Oxford, and finally to a wedding just outside of Ipswich from August 25th to August 31st.
For context, we plan on exploring as much as we can. My partner and I fell in love with castles during our trip to Switzerland (the U.S. just doesn’t compare, right?), so we’re excited to visit Cardiff and Warwick castles. We also want to experience at least one winery walking tour, visit some museums in Oxford, and hopefully squeeze in some hiking, schedule permitting. Thank you all! 🙂
It sounds like you have an exciting trip planned! Here’s a more detailed packing list tailored for your last week of August in the UK:
Clothing
Accessories
Miscellaneous
Toiletries
Documents
Weather Considerations
It sounds like you’ll be having a fantastic time visiting castles and exploring! Have a great trip, and enjoy the wedding!