I use small zip lock bags, with a white write on area that takes Sharpie marker writing well. I use them when I gift away small quantities of chemistry, and, depending on the item, either ship the baggie in a larger jar, or ship a small vial or bottle in the baggie.
I tend to include a 8.5x11 sheet of full instructions, and label each item similar to: Part A, sodium sulfite, 1 pinch per 750mL of 125F hot water , part B metol, full packet to water with pinch of part A, stir to fully dissolve, then add balance of part A, then on to part C, Hydroquinone, add after all of part A is dissolved with stirring, etc.
The baggies only get the ' Part A Sodium Sulfite'. The rest goes in the full instructions.