I use a 2 cycle oil container that has graduations in ml on the side of a see-through part of the container. You can buy containers of 2 cycle oil that dispense (think it's) 55 ml (cc) at a time into an upper container.
For most other stuff I use a measuring cup that has graduations of 1 tsp, 2 tsp, 1 tbsp on it. These are available at lawn and garden areas. Some stuff like Roundup come with a cup with graduations on it. These are all plastic.
Get one of those converter lists, available on magnetic backing, that show the conversions from ounces, cups, ml, etc. One gallon is 3781 ml. A 40/1 mix into 1 gallon would be roughly 90-100 ml.
Ralph