Once you have some essential painting supplies (key mixing colors) you may wish to buy some other acrylic paint colors, etc.
I recommend having tracing paper (large pad) as this has many uses including providing a key part of an acrylic palette. The palette (next post) will keep the paints from drying out for at least a day. Parchment paper or butcher’s paper have a lot of uses as well. While I use quite a bit of newsprint for printmaking, pads of this are expensive for what you would use it for and if you have a need, buy loose sheets in bulk. Chalk dust (marble dust) and other fillers may be added to gesso or matte medium to create effects that are normally achieved by using expensive commercial products. Golden has some great choices: pumice medium, clear tar, modeling paste, and also offers some fluid additives which change adhesion and viscosity. Dick Blick, again, has the largest selection for artists but if you are looking for fillers, dry pigments and a lot of other really great stuff, I have two stores in S.F. that are wonderful and they ship: Sinopia and Douglas and Sturgess.
Additional acrylic paint colors that you may want to add: yellow ochre, burnt sienna, ultramarine and cobalt blue. Zinc white is a more transparent white and can be useful. Using black, white, yellow ochre, burnt sienna, and ultramarine blue will give you more subdued and traditional color mixes. There are too many color choices to mention. I also have black ink (Super Black) in the photo and that can be useful in mixed media work. Flood brand “floetrol” is a commercial paint additive and eliminates brush marks and improves flow in house paints. This is not added to tube colors and I will explain it’s use in later posts. Finally, you may wish to buy clear acrylic gesso. This is an expensive product but it dries clear, has some grit to it and is wonderful for separating layers in a painting, maintaining the integrity of the paint layer.