When we were out on a long day out, for the last 2-3 years we’d have his bag with us. When we thought he was getting tired or bored, we’d put the bag down flat on the floor (standing it up) beside him, roll up his lead, then pick him up, tucking in his tail and put him bottom-first with his front feet to follow.
One of the best things in the world was seeing his subtle tail-wag as he realised that he was getting into the bag: as it went down on the floor, he’d let out a little gleeful wag which meant we were right to thing it was time for the bag again.