Marta asked for drabbles about preparations for journeys.
Merry, stacking cupboards, putting pictures upon walls never meant to be long lived in, knows this. He counts coins, knows the price of ponies, measures meals, miles.
For Frodo is leaving, and Merry's heart hammers in his chest. Fear, yes, but he's a Bucklander, too: walking the hobbit-ways of the Old Forest, he whistles, for the woods whisper of Outside...
The 'wizardly dent' refers the dent Gandalf banged into the door when he knocked the thief-sign off of it in "The Hobbit."