Bring a backpack to London. I repeat: Bring a Backpack.
When you’re going on weekend trips, you’re most likely going to travel on the cheap, so your flight will probably be early in the morning or late at night. This means, you won’t be able to check into your hostel or hotel until mid afternoon. If you don’t bring a backpack, you’ll get really sick really fast of carrying around a shoulder or crossbody bag through your first tourist activities.
When you’re packing said backpack, pack light. For a weekend, all you need is underwear, one pair of jeans, a pair of leggings, one or two going out tops or dresses, and a couple of toiletries. Don’t forget your cell phone charger, and make sure to top up before you leave town. Make life easy on yourself by only bringing what you absolutely must have, and remember to rewear and layer your clothes. If you’ve got a travel towel and flipflops, definitely bring them for the showers.