British airways personal carry on bag

I should have clarified that the bag in question is the personal item other than the carry on allowance.

Exactly which RS 'backpack' ?

https://store.ricksteves.com/shop/travel-bags

How big is your other bag? We carried our Appenzell bags on, but they were larger than our "personal items."

All flights
Adults, young adults and children

1 handbag/laptop bag (max. 23kg / 51lb and up to 40 x 30 x 15cm / 16 x 12 x 6in)
plus
1 additional cabin bag (max. 23kg / 51lb and up to 56 x 45 x 25cm / 22 x 18 x 10in)

The above the BA site---https://www.britishairways.com/en-us/information/baggage-essentials/hand-baggage-allowances

Last I checked, BA's personal item size was 12" X 16" X 6. They do check and tag if the flight is full, as they won't accept any personal items in the overhead bin. If the flight is not full, they are less concerned. If you pack the bag so it can squeeze down into the above size you will likely be OK. If you mean RS full sized back pack, then you are likely pushing it even if you can, in theory, squeeze it down to the correct size. I always fly BA internationally, so my bag is exactly on target. Besides, much larger than that really interferes with your leg room.

I have used my RS Civita backpack as my personal item many times. I like to fly BA because they are more generous in their cabin bags than most other airlines. You should be fine.

I should have specified the Civita pack rather than "small". Anyway, thank you for all of your responses. I'll make sure I don't pack it full.

No worries! The Civita and the Appenzell both work as underseat bags. There are lots of good underseat bags. Patagonia lightweight travel tote (on sale), etc.. If you have extra money to spend - RedOxx gator bag. Tom Bihn synapse 19 backpack. Most "soft" packs are compressible and not an issue. Stick with 20 liters or less. Zip-top tote bag. You have a lot of options here. You only need to be concerned about the size of the carry-on going into the overhead bin. (Provided you stay under 22 liters for the underseat bag.)

I am looking for a cross-body/long strap bag that fits the BA personal item requirements. I had already purchased a perfectly-sized personal item backpack for an international trip then was gifted the eBag TLS Mother Lode. I absolutely loved the versatility of the Mother Lode for my main bag/carry-on and now am on the hunt for a crossbody bag that's the max size of a personal item so I can carry them at the same time without a backpack on the front, with as much room as possible to bring home souvenirs and gifts. Any recommendations? Packable is another plus (though not required), as I haven't needed it on the way out, just traveling home.
So far I've found:

• eBag Haswell tote (couple inches short on length, but best bet so far?)
• Made by Design Duffel (Target)...technically too big, but soft so squishable?

So many others are either much smaller (purse) or too big (messenger bags).

cacitaly2017, I too have used the Civita for years now as my personal item. The photos on the website are a bit misleading, because it looks stiff and firm like a kids school backpack. The reality is that it is soft and frameless, like sun-baked says, with about the consistency of a pillowcase. Empty, it is limp and squishes down to very small. So the actual size in use depends on how much stuff you put in it, and the shape of those things.

I've used the Civita day bag as my personal item for many British Airways flights. No problem. And sometimes I really pack it full too!