SanDisk Ultra USB 3.0 flash drive. Suitable for use as a cheap Windows 10 Recovery Drive (for those of us who upgraded and don't have bootable installation media if the system crashes). The read speeds are OK but the write speeds are slow, so don't buy it if you want to write often, but should be OK as a backup. Packaging says "up to 100 MB/s". Plug in the stick, type "recovery drive" into Cortana, click the top link and tick the option "Back up system files to the recovery drive", then just follow the prompts. It will prepare the files (can take a while) and then ask you to choose the right USB stick before copying anything.
The stick has a hole for a label or keyring, but the plastic is lightweight, so not one to carry around everyday.
Use Click and collect online to get this at £4.99 (it was £6.50 in the store I went to). Seems a good price for 16GB even compared to online. I think the deal is nationwide, stock was OK in West London or for home delivery.
I also noticed that the 64GB SanDisk Ultra Fit (tiny) USB 3.0 was £12.99 in store, but £13.99 online, the packaging on that one says "Up to 150 MB/s". You can find better value online but not bad value if you want one today.