If you ask most people what there number one food memory while in Luangprabang is, odds are the answer is likely to be the food market that springs up in the evening. It's down a narrow corridor between two larger buildings. You'll find yourself dodging other food-goers and quite often shoulder to shoulder as you pass other people as it is usually busy.
On top of all that it's inexpensive. Most of it is quite good (though not all) but like anything else you have to explore and find the best. Feast!