Good suggestions all. As a backpacker, I carry Gatorade mix for use with water that I filter. I also make up individual packets of instant coffee and sugar for the mornings.
Because of weight, what I do is take a plastic sandwich bag (the cheaper, the better), and place a single serving of whatever into the corner. I heat up the blade of a very sharp knife and cut the edges of the plastic bag to size, then pinch the edges together creating a seal. This creates a seal from the melted plastic. Be sure leave extra space in the bag so you can cut it without burning yourself and the package isn’t under much pressure.
You can also “double-seal” it using a lighter or a blow dryer/heat gun along the sealed edge. Heat slightly (until melty), then pinch together. Don’t burn yourself. Be sure to “test” the new seal to May sure it doesn’t leak.
Because the new “bag” is so small, it’s easy to tear a small side open and pour into a water bottle or cup. Very easy to do. The individual servings hold up well when I store them all together in a good quality Ziplock bag. Works well. If you have a vacuum food sealer that works great but the bags are a bit heavy and expensive. I use mine for dehydrated vegan meals I make for the trail.
Here’s a pack with Gatorade to take with me when I’m out. Because weight isn’t an issue unless I’m backpacking, I leave the ziplock part of the bag for slightly better storage. This is about a quarter of a “snack-size” bag. (2 Euro coin for scale)