My reasons for checking my backpack are as follows:
1) can’t take trekking poles as carry-on
2) budget airlines do not allow any leeway on the size or weight of carry-on.
3) they also charge for hold baggage, and if I’m going to pay extra to check my poles, I may as well check my pack as well.
4) I need a pack long enough to accommodate my poles.
I don’t think my pack is too big: 33l, expandable to 40l if you stuff all the outside pockets. I don’t expect it to be full, and hopefully not too heavy: all my clothes will be ultra light and quick drying and I’m not going mad with the number of items (2 long-sleeved, 2 short sleeve, 2 trousers, 1micro fleece, rain jacket, hat, buff, gloves, 3x underwear and socks), no books except
Brierley and a small notebook, dual-purpose soap rather than different detergents for everything - but it is too tall to go as carry on. That decision is made now, the pack is bought (and is very comfortable).
So, thank you to those who have made practical suggestions. I have wondered about the wrapping service at the airport, but the alternatives are worth exploring too. My pack has a built-in rain cover..... but if that got torn in transit, I then wouldn’t have a rain cover.
I will be wearing my boots on the plane and carrying valuables, medication and Travel documents in an extremely light collapsible bag. I have a night booked in Bayonne because my flight arrives in the evening. I am travelling via Paris, but with a 4 hour connection time, so hopefully all will be well re lost pack. I’ve also only known it once in 30 years as a regular traveller.