if you want a huge grabbag of miscellaneous assets, I'd recommend looking at
https://opengameart.org/
It takes time to rifle through to find what's useful to you, but there are a few quite good artists who released good amounts of stuff into the public domain, like jetrel,
A collection of RPG items. The intent is not so much for these to be used as inventory items, but is for these to be used for environmental decorations on the interior of a house/castle/shop.
opengameart.org
hyptosis
Some SUPER old goblin themed cave tiles. Was making a kind of goblin themed Dwarf Fortress but it didn't get very far. Use them for whatever you want, have fun!
opengameart.org
and ansimuz
Video Preview A Pack of Pixel Art Assets for Zelda Like Game Development. Includes: A female character with walking and running animation in all directions. A Tileset with animated tiles for the water areas A portrait of the Character
opengameart.org
and there's other stuff that's licensed under common CC-BY / CC-BY-SA or whatever licenses as well. For instance, the Liberated Pixel Cup art set is CC-BY-SA, and has a lot of tiles (
https://opengameart.org/art-search-advanced?field_art_tags_tid=liberated pixel cup ), and was made by Sharm (well, with additional artists, there's a bundled credits.txt for who you need to credit to use them)
If you start seriously tinkering with the engine and want to spend money on addons, I'd say that the $30 for the complete yanfly set is probably the best deal around.
In terms of sprucing up how your maps look, buying
doodads on its own is a steal at $1; being able to place little decorations off-grid can instantly make things feel less artificial, even if you aren't using any additional assets.