It indicates that Huck frequents places perhaps grocery stores where the conditions are not sanitary what with "sickly eggs and rotten cabbages and dead cats" in other words, Huck cannot afford to frequent fancier shops or fancier homes because he is poverty stricken and used to such sights.
Answer: Smile is a very common expression. It is one's feature into an kind expression, it usually looks like the corners of the mouth turned up and the front teeth exposed.
