Here's a breakdown of the different items available for purchase in the Booty Boutique:
---- REQUIRED ---- sign :5 mirror :15 saw :25 ship's horn :40 map piece :figurehead trade ---- OPTIONAL ---- feather pen :10 wreath :20 pirate hat :30 hub cap :50 rock and roll plate :199
The "optional" items are useless, and the antique dealer will let you return any of them for full price. The "required" items cannot be returned once purchased.
The fact that items can be bought and returned like this lets us break the game in an interesting way, and it involves polishing Frank's peg leg. Essentially, Frank will continue giving us money, so long as the amount we are currently carrying is less than 5,912. This is meant to stop us from chartering Captain Kate's ship, which costs 6,000 pieces of eight.
But if we were to, say, buy the collector's plate, then spend several hours grinding the peg leg until we have at least 5,801, and then sell back the plate, we'd actually now have enough for Kate's ship! This means it's (theoretically) possible to skip the spitting contest entirely, but it would be extremely slow and tedious to actually execute.
However, if we were to skip buying the drinks from the Bloody Lip using this trick...
...we'd end up softlocked later in LeChuck's Fortress.
The programmers apparently didn't know what the rectangular beige object behind the counter is supposed to be. When moused over, it will be tagged as either "sword sheath?" or "cheese grater?". The game flips a coin to decide what to call it every time you mouse over it.
Even the antique dealer doesn't know what it is.
The parrot will say something if we try to talk to it, but it says something different depending on what's been said most recently!
The way this works is that every single item in the shop has a unique "parrot line" assigned to it. Looking at an item will make it so the parrot says the corresponding "parrot line" the next time Guybrush talks to it. The same also applies to several dialogue options with the antique dealer.
The majority of these "parrot lines" are just repeating a word or phrase said by Guybrush or the dealer, but sometimes the parrot makes jokes or comments about the item, or mangles what the dealer said into something nonsensical.
In total, there are 37 different lines you can get the parrot to say.