In the 1980s banks and building societies (but mainly banks) were desperate for the business of youngsters. We just wanted the free stuff.
Sadly, I never got the Nat West pigs, but I did get a sports bag holdall and other paraphernalia (including folders, & a pencil case) from Midland Bank when I opened up a Griffins Savers Account. And I still have the bag! I might even have the other stuff somewhere. Am I still with the Midlands/HSBC? Nah, that account got closed years ago. I've had other accounts with them since, but not right now.
Okay, this isn't a great picture of it, it just happens to be one I already had on my phone. I'll dig out the bag sometime and take a better picture.
But is it collectable, and what is the value?
Whilst perhaps not as sought after as the aforementioned piggy banks (let's face it, they'll look nice on a display shelf) these giveaways do find place in the heart of collectors. If you have the complete and unused Midland Savers Stationery Set and Sport Bag in good+ condition I would imagine this to fetch a 3 figure value. Various parts of the stationery set (pencil case etc, folders, badge) can be found on eBay for a few pounds each.
As for the bags, there are a few of them out there, and I've seen them go for either side of £15. Personally, I think the value should be higher than that, and it's about timing and listing it right. If I was putting this bag alone up on eBay I would probably start at say £20 and see how it goes. At the end of the day, as well as being collectable, it's also a perfectly usable bag.