As I've said in other posts, I tend to like to work with my hands, rather than with traditional art media (i.e. pencils, pens, paints....the 3 P's I guess).
My one fav art supply ended up turning into 4 because I couldn't decide on just one and I like to change what I'm using often, so I fall in and out of love with supplies quicker than I eat a bourbon biscuit.
I use a lot of rcoks/pebbles, cork and foam in the bases of my Warhammer models. Which it why I would say they are some of my favourites, as they are so versatile. You can just stick them down, paint them to suit the situation, glue them in stacks and no two bases are ever the same. Take a look at the my friends Warhammer model Instagram posts Tiny Strokes for examples of what I mean, he's a great artist and amazing at what he does. Foam, I love foam, you can turn it into anything, you want cosplay armour, it'll do it! You want weapons for LARP, you betcha! You want to create a bombed out road, you best believe you can! Faux flowers are on my list, as I've gone head first into making flower crowns and using flowers in hats. I'll post a list of what and where I get these below (most won't be affiliate links but its always good to support small businesses and I get the faux flowers from a great little company).
Rocks - Not Affiliated - https://www.ebay.co.uk/itm/WWG-Sand-Miniature-Basing-Kit-Wargame-Terrain-Model-Scenery-Diorama - I like using warhammer or war gaming basing materials and this shop has everything I need and use.
Cork - Not Affiliated - https://www.ebay.co.uk/itm/CORK-SHEET-225-mm-X-195-mm - good sized cork sheets, i use it for model bases mainly.
Foam - Affiliated - https://amzn.to/2XJU4Am - good sturdy foam board, great for scenery.
Affliated - https://amzn.to/2Ut1So3 - EVA foam mats, perfect for making cosplay armour.
Affliated - https://amzn.to/3e0c5jL - thin foam, perfect for model bases and details on cosplay armour.
Faux Flowers - Not Affiliated - https://foxflowers.co.uk/ - cute little online shop in the UK, super realistic plants, I use them mainly for greenery.
Personal Score - Like 2/10, I was a half arsed with this, as it was just my favourite things to work with, none of them being drawing implements.