Portable Stools for Photographers

I've got a couple of these lightweight, canvas, fold-up seats, and they come with a carry case. They're lightweight and you can sling them over your shoulder to carry. And they've got a cup holder in one of the arms. Cheap and cheerful, and better than nothing.
https://www.diy.com/departments/molloy-multicolour-metal-camping-chair/1860857_BQ.prd
https://www.diy.com/departments/molloy-multicolour-metal-camping-chair/1860857_BQ.prd

During my misspent youth, I attended (and raced at) motor racing circuits all over the country and I'd say that while a portable seat of some kind isn't a bad idea, it will only be any use if you can find somewhere flat(ish) and reasonably firm to put it on.
Otherwise, you'll spend all day straightening it up and/or pulling the ends of the legs back out of the ground.
Portable chair for tightwads.
(I've got two!)
Otherwise, you'll spend all day straightening it up and/or pulling the ends of the legs back out of the ground.
Portable chair for tightwads.
(I've got two!)

Thanks for the comments so far. I would just mention that I am not on a tight budget so do not let cost restrain any recommendations. I am also aware that a number of these "stools" do not have a problem with sinking and for some there are attachments to deal with this real potential issue. Although I initially need it for this one event, I expect to attend other events where it will also be useful.
Dave
Dave

Walkstool is a great product, designed and made in Sweden, they have 3 legs and pack away really small and light. You can also get a base to add stability at the ground level which helps with the sinking problem.
I have one and it is always on the side of my camera rucksack, perfect whilst waiting for the dawn light.
Not cheap but you get what you pay for.
I have one and it is always on the side of my camera rucksack, perfect whilst waiting for the dawn light.
Not cheap but you get what you pay for.

Thank you for the walkstool Ian - as someone who frequently needs to sit to rest my back - I sent for one and a) it is not too heavy for me to carry, and b) extremely comfortable and feels very safe. I think I may soon be able to venture back outside into the big outdoors. Second vaccination next week so probably as safe as I can be. Many, many thanks. And also for Dave for asking the question.