Personal item when using a backpack as luggage

I like the Sea to Summit Sling bag. It packs away into a tiny keychain bag. It’s great for true one bag travel. I like it because it zips closed.

The cross body design works well with a backpack.

Here’s a review with photos of it stowed.

Amazon has some foldable lightweight totes that fit many underseat measurements. Take a small crossbody purse for day to day that will fit in either other bag for flying.

I carry a cross-body bag as my personal item when I travel with my Ebags Weekender backpack. There are a variety of sizes out there so you can find the one that best fits your needs, particularly for daily touring use when you don't have the backpack with you so you have a place for money, sunglasses, water bottle, travel paperwork, book or kindle, etc.

LeSportsac has a fairly large "Everyday" cross body bag. It seems cavernous to me, but I lean toward smaller and carry their "Classic Hobo" cross body bag. I love mine because there are a lot of zippered sections, extremely lightweight, and water resistant plus machine washable. There are lots of options in bags there.

Ok, let me wax poetic about the SeatoSummit UltraSil daypack (I had to check that Cindy wasn't referring to the same thing ;). It weights 2.5 oz., carries 20L of stuff, and stuffs into a tiny little stuff sack creating a ball that can fit in a jacket pocket:

https://seatosummitusa.com/collections/day-packs/products/ultra-sil-day-pack

How we use it:
My family of 5 (3 t/weens and parents) travel with an Osprey Porter 46 backpack as carry-on luggage, and a SeatoSummit UltraSil daypack. Take my daughters recent trip abroad. She would be flying on airlines that limit carry-on weight to 18lbs, but she needs to bring books and gear and shoes, plural. We packed her Osprey with everything she wanted (we pack the wants first, and then edit down to needs to fit weight restrictions). Her bag weighed 25lbs. So we got the UltraSil and put two books, camera, pair of Chaco sandals, rain jacket, snacks, water bottle (empty), until it was full of the heaviest items. We weighed the Osprey again and it was 18. We got 7lbs into the UltraSil
The game-plan for us is to pack the UltraSil with all the stuff that will make our carry-on look and weigh the right size BEFORE SECURITY. Then, once through security, we load everything back into our Osprey that we dont want access to on the flight. The UltraSil will go under the seat, but not loaded with all that stuff.

So if you pack less than 25 lbs (this was unusual - she needed the bound books), you can imagine how you could bring home a few Souvenirs using the same method.

Once we are in Europe, we carry one or two of the UltraSil's with us out and about. These go in my pacsafe crossbody-type-bag (which goes in the UltraSil through security), or in a pocket, so that we can carry groceries or whatever we might purchase (we usually stay in Airbnb's), or we use it to carry non-valuables (relatively) like rain jackets, or towels (if going somewhere with a beach). Again, the bag weighs 2.5 oz. so a lot of bang for no additional bulk.

Are you talking about bags when flying? Beware, many airlines in Europe, especially the cheaper ones, are one item only.
You are not allowed a backpack and a "personal item", it is one or the other, not both.

I would just pack one of these in your backpack and carry the smallest crossbody that’s comfortable for your daily walking. When you’ve acquired items, you can pull out the bag and begin to use it. I like this bag for taking to the grocery store, too. It’s heavy-duty, holding our beach towels, sunscreen, etc. when we’re in Hawaii, and it’s easy to wash.

https://www.amazon.com/gp/product/B0028K2ST6/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Pay heed to Chris F. Carry-on regulations vary according to carrier. The short-hop European airlines tend to be stricter. easyJet, large and very successful, insists that one carry-on item is ONE; not a backpack and a shoulder purse and a laptop computer. Some will allow extra stuff, at extra price. If you want that option, be sure to purchase on-line ahead of time; the prices can be much higher at the gate.

How big of a cross body did you want? I bought this for my daughter and she really likes it.
https://www.amazon.com/gp/product/B01DM3NG1Q/ref=ppx_yo_dt_b_asin_title_o09_s00?ie=UTF8&psc=1
Its dimensions are 18L x 11H x 8W inches and weighs 1.4 lb.

I really like Kipling bags. This is the Erica: https://www.kipling-usa.com/erica-crossbody-bag/HB3122.html#
The dimensions are 12.25"L x 8.75"H x 6.25"D.
The nice thing about this cross body is that is has a nice depth.

If you go to the Kipling site you'll find they have many options.

Thanks all! We fly with British Airways, so we're allowed a carry-on of 24x18x10 and a personal item of 16x12x6. Carryon goes in overhead, personal under my seat. My current plan is to use my day crossbody purse going over and have a packable tote for the return (I can always pack the crossbody in my carryon.) Problem is, all he packable totes I'm finding are all too big to be considered personal items. Will check out the Sea to Summit suggestions. Thanks, again, and if anyone has further brilliant ideas, please let me know!

Ikea "knalla" sports bag for $4.99 is packable, squishable, small.

I cannot vouch for this bag, but I found it when looking for my carry on.

https://www.amazon.com/WANDF-Foldable-Lightweight-Luggage-Resistant/dp/B07F68J66Q/ref=sr_1_4?keywords=packable%2Btote%2B16%2Bx%2B12%2Bx%2B6&qid=1562476070&s=gateway&sr=8-4&th=1&psc=1

Emily, keep in mind if you buy a lightweight unstructured foldable tote and don't fill it all the way, it should still fit into the tester frame and be malleable enough to fit under the seat. Or if you have a sewing machine, you can make it smaller.