Keeping a studio well supplied is not always easy. Cost can be a major barrier, since I must purchase all the materials up front, not knowing when or if a sale will result to cover the expense. Scrimping may be necessary in lean times but if I do sell something I try to remember to keep stocking items I'll need. An artist friend of mine, Linda Rowell-Kelley, keeps her studio stuffed with fresh canvases of every size so that she'll always have what she needs when the inspiration strikes. I also try to have at least a few canvases of varying sizes handy, as well as frames for showing.
Buying quality paints is key
I never buy student grade paint. The low pigment content will always leave me disappointing in the final results no matter how inspired the subject. Paints can cost upwards of $30 for a tiny tube, but they usually last much longer. I have had some tubes of paint for over 10 years! Cadmiums are quite pricey but I prefer them for their intense pigments.
I also keep an abundance of brushes around. I am pretty hard on brushes since I sometimes mix with them, so allowing myself new brushes is key to keeping things running smoothly.
I have a rather small studio space that I reserve for indoor painting. That space is really for keeping the paint, canvas and brushes handy. I store completed work and large frames in a different room, out of the way. I have built in shelves in the studio where I keep the canvas and frames. The paint is stashed in a rolling cart that also serves as my palette. The brushes hang on the wall. It's important to keep organized otherwise the studio does not feel welcoming. I also keep my french easel packed and ready to go with a separate set of paints and brushes so I can just grab it and go when the weather is right for outdoor painting.