The Douane chappies are a bit hit and miss. Most of my customers who have travelled to Blighty and back have had no problem smuggling my mole traps and auction win vintage reels over, but they seem to give anglers a hard time. To be fair there is nothing that you need that you cannot buy here.
Decathlon shops are all over the place and stock pellets, boilies and groundbait. Also
www.pecheur.com can send bait to a point relais close to where you are staying with no delivery charges. Supermarkets and garden centres stock milled maize in 5kg bags. If you pour boiled water over the milled maize and then add crushed hemp and maize groundbait from Decathlon or Pecheur that is all you need for the feeder. Hookbait is banded Frolics dog biscuits or sweetcorn, both from the supermarket. If you want to go exotic buy whelks or prawns from the fish counter. It really is that simple.
The gaves are mountain fed rivers, cold and very clear. I would suggest taking fine hook lengths and small hooks. Buy some maggots if you can find a tackle shop. They are very expensive, but might be useful in the clear water and blue sky.
Also, be aware that there are brown bears around Pau. The type the Yanks call Grizzlies. If you discover a steaming great pile of poo in the woods it might not have been left by a barbel angler