I love the NGA. I may even have spent more time in there than in the Met even though the Met is much closer to me.
I think the thing about your rucksack has a practical reason. They are worried about people absentmindedly turning around while in front of a painting and damaging the painting with the rucksack. I don't ever recall the NGA staff being rude or crabby to me. (VERY unusual for a collection of government employees!)
ML/NJ
I hadn’t considered that as a reason - they did tell me I couldn’t wear it over my shoulder. Color me slightly chastened...
:-)