What's the best way to clear out my inventory? I'm quite a newbie and I'm not sure what to do with the items I've collected exploring.
I've put some things up for auction but that isn't a guaranteed way to get rid of things (and I'm not sure of pricing anyway oops).
Are any items basically junk? What items should I be holding on to?
I want to collect every interesting little thing I see exploring and I've had to leave behind some blueprints due to full inventory already. (Also, what's the best way to go about collecting the materials and money for Warehouse level 2?)
If there are guides that could help me, I'd appreciate them but if not, any advice is welcome!

Thanks in advance!

Depending on how you value apparel, apparel-crafting items are useless until you get a Tack Workshop built. That's Bones, Crocotta Fur, Flame-Forged Scales, Biogas Bubbles, Emeralds, Sapphires, Leather, Living Wood, Elegant Feathers, Plain Feathers, Topaz, and Wing Membranes.

I may have missed some, but it does add up to a lot of space that you need as a newbie.

Otherwise, use all the blueprints and schemes that you have in your inventory to move them to Craft and Construction. Then they won't count as space in your inventory. It doesn't matter if they're too high a level, they still move. If there are blueprints or schemes you've already used to their maximum (6 for Blueprints, 1 for schemes, or just buildings you've made already), then you don't need them anymore!

As far as finding materials, I use the Island Exploration Guide in Player Guides to make sure I'm going to the best islands for the materials I'm looking for. Clay is most common in Grassland or Volcano, Wood is most common in Grassland or Savanna, and Stone is most common in Volcano or Desert. The Travelling Market is also a good way to get materials if you get lucky, and those are most common in the Jungle or Volcano. Although most of these recommend Volcano, I will mention that the Volcano does not drop any food items.

And, the higher level pets you use to explore, the more silver they'll pick up from the ground and from chests.

Thank you @StarlitWoven, that helps a lot!

Unfortunately, BK doesn't use @'s, but you're totally welcome! Let me know if you have any other questions :)