I choose to take my tent because I knew I'd be away for 14 days, I plan to use my bivi next month on a shorter trip.
The 'downside' of the route I took was that for the first 4 days their were no camp sites so had to wild camp. For anyone contemplating the GR11, Bera is first town. I found a good spot, as you follow the GR11 red flashes up the main street, a few 3 seater benches to your left, the route suddenly takes a 90 degree turn (bar on your right) so you just walk up the hill on the narrow tarmaced road. In a short distance, this road intersects with another narrow road with a large modern house to your right. On the opposit side of the road you will see a footpath, wall on the left, fencing on the right of it. Walk along the footpath about 50 yards and you have your wild camp spot. It obviously was planned as a picnic spot by the town but it was never finished. Plenty of grass, a couple of small tarmac areas and two three seat benches PLUS piped drinking water, the press button type tap is there and it works well. I shared the small area with a young German couple.
When I got to Elizondo, I stayed in a Spanish Pension, a dormitory bed for 15 euros, next door a bar and food. Not bad but very hot that night.
The next night I met the German couple again at the Urkiaga Pass, nothing there except a hut, only a few months old I think. It was open with a two bunk bedroom (which the youngsters used) and I sleft on the 'lounge', just a larger room with a table and two benches, all for free! This worked out very well.
When I walked to Uritz, the first real camp site is down a straight road for 2km. I stayed there and it was very good. The downside was that to get on my route again I had to walk 2km back in the morning. On the French side campsites were all in the right places. I particulary recommend the one in St Etienne de Bagorrie. Well looked after, good toilet/shower block, next door is a small supermarket but best of all the charge was 4 euros a night!
The next best one is at Biddaray, you come down from the GR10 at at the village the walk goes left. I turned right, through the village, past a restaurant where I ate and drank later (very good) then turn a bend to the left and directly in front of you is a one story building with a large lwan in front. You can pay 20 euros to sleep indoor, with breakfast the next day, or like me I slept in my tent for 4 euroes on the lawn. There are also camp sites at Ainoaha and at Sare.
I got caught out once in France, ran out of cash at Bidderay and then found that the next cash machine is at Sare. My wife is never happy if I use my debit card abroad.