This literally means “of rigor." It's a common French phrase that implies that something is "necessary according to etiquette, protocol or fashion"
De tout un peu et de peu pas beaucoup
A little bit of everything, as in, you can have a little bit of everything in moderation
A form of French entertaining; half dinner, half cocktail hour. On an invitation, the name denotes that you will not leave hungry, but should not expect a formal sit-down dinner