One way I keep our art supplies somewhat contained is by using this cart from Ikea. I am able to roll it away to the closet to store if I have to (like when we have visitors), but can also keep it out to let the kids have access to it. We can also roll it to our kid table, coffee table, open space, out on the deck, or to the kitchen table if we need, which is fantastic for accessibility.
Open-ended art art allows kids to work on numerous skills such as:
Fine Motor Skills: Kids can use scissors to cut freely and explore (unlike a craft where items tend to need to be more refined and exact). They are able to use all kinds of drawing utensils to make their own unique marks.
Language Development: When children create their own art, they use language to explain to others about what they have created. They may use shape words, colors, and more to describe their work.
Decision Making: Kids make decisions about what they want to use to create their art and how they will create it. They learn how to problem solve to figure out how to put what is in their heads on paper without the help of adults.
Visual-Spatial Development: Kids develop their visual-spatial skills by working with different art supplies like stamps, beads, googly eyes, pipe cleaners, etc. They have to develop coordination to be able to mold items to their liking.
Confidence and Open Ended Thinking: Children learn confidence through open-ended art because they learn that there is no one way to create art. They are able to explore multiple ways of creating and doing.
Here is a link to a great studies about how important art is:
Here is a list of items I have in our art cart.