Things I use as a new DIYer and would love more of:
Glass bottles, as Rick pointed out. All sizes (down to 10 ml and up to 30ml for me, as I haven't stabilized enough to want huge bottles)
Syringes, all sizes. 1,3, and 10ml work great for moderate sizes. Also, clear nail polish to protect the numbers, as they wear off from use.
In a related note, blunt tip Luer loc(k?) needles. They come in different gauges (diameters) and lengths. You'll want 14 gauge or less for VG, and PG/flavorings can be OK with smaller needles, but I just use 14 for everything. I wouldn't mind several dozen of these, but 3 is enough to get by. Long needles would be nice in certain situations, I think mine are all 1.5 in.
Also glass droppers with a removable rubber piece would be nice, but I don't have any.
I'm sure there are plenty more goodies that would be nice, but the above are pretty essential. I apparently like to live on the edge, and mix 100 mg without any safety gear.