Normally I pick a theme, find every possible item that exists for it on site, and just start mass buying/filling until I have hundreds of items. Its a good method for ridiculous TC hoarders that's served me well for years.

But lately I've been branching out and getting more creative with my TCs as I've literally begun to start running out of possible huge TC themes. Yellowstone started the trend of ridiculousness pretty simply with basic sections for different "themes". Next up was Oompa Loompa, whose TC was planned out entirely in advance so I could build it from bottom to top one row at a time. But Into The Woods absolutely takes the cake. I'm doing a visual retelling of a play for him so I started by re-watching the play and taking four pages of notes. As I fill up his TC I go through my notes and check things off as I buy them, which isn't too bad. But sometimes I need to rewatch a scene so the desk ends up like this as I furiously search Subetalodge, arrange items, and add to my notes while trying not to miss any details.

I can't be the only one going to ridiculous lengths. Tell me about yours!

It depends on the pet for me.

Are they hoarders, or do they have the means to have a lot of stuff? Patchouli, Sakuya and Flandre all live in a very rich, comfortable mansion, so they have a ton of space and wealth to have a lot of things. They all have stuff that addresses their hobbies, interests, general state of being, the kind of food they eat, the kind of stuff they wear, their relationships, and the kind of powers they have. Actually, Patchouli's got the biggest TC out of all my pets because she's a librarian that collects pretty much any book that's remotely interesting to her or has some sort of historical or cultural value. It's a bit ridiculous, and fairly expensive.

Other pets have stricter, themeatic things that I'm trying to keep simpler in comparison. Hexer's a dark mage in employment by a royal army, so she has a lot of spell-stuff and magic tomes to work with, but her personal life is represented a little less by comparison. In that vein, there's a few things relating to her religion, and then her small collection of trinkets and keepsakes involving her girlfriend. Some of my pets aren't materialistic much at all, like Sariel; she owns very little besides her basic equipment for daily work, a few items involving her personal relationships, and a gathering of offerings/relics intrinsic to her being such as silver coins and chimes. She just doesn't see much value in material things, and I like having that reflect in the nature of her treasure chest.

And then sometimes I really want to just tell a story + represent important things in treasure chests, and do only that. Sure, I could collect all sorts of dusty things and golden flowers for Genocidal or Asriel respectively, but I've found that there's a more poignant nature to having fewer items represent their stories and themes. Bits and bobs of their former lives, and things that represent the stages of the current situation. A personal belonging of significance here and there-- the two lockets, the knife, the knitting needles and cracked photo frame. It all comes together in a very specific way that I like a whole lot.

I put a metric ton of thought into pet treasure chests, but they can be anywhere from excessive to simple depending on the character's world and the way I'm presenting them.

It depends on the pet to be honest.

I most the time start with a character concept (so all of mine are OCs ) and write down a bit stuff about then. After this is done I decide what they look like, what they wear, what they like, what is important in their life, which setting they are in and start looking for TC stuff which fits in regard to this. SO I fill mine with food they like, clothes they wear or things important in their live.

Feel free to have a look at some of my TCs and the stories of my pets (Like Marcius, Yago, Milan, Laertes and Navarre) to get a better idea what I mean =)

For me it is all about the story/theme I am doing for my pet. Once I've came up with a design and story for my pet I then find the TC items for them. I just go to Subeta Lodge to find relevant items. c:

For me, what works best is to do the pet's story first, then go back through the story with SubetaLodge open in another window and search for whatever I can think of that relates to each bit of the story. But then in addition, I do what you were talking about with the theme, so most of the pets have some theme of items they collect. Like Drifblim's is donuts, Al Cody's is cowboy stuff, etc.

Tak is my main pet for everything (reading, feeding, battling, etc.) so his is the biggest. Besides stuff related to the two books he's in, he has every skull, spider, scorpion, and vulture item I can get, plus Stephen King tribute items. He's a spoiled lil demon lol.