For salads, mix everything together with your fork and then try to take a small portion of each item and place it into the capsule. If you are served dressing on the side, be sure to stir it and put a small amount in.
For burgers, hot dogs, anything on a bun – be sure to take a sample from the underside of the bun and a small amount of everything in it (meat, veggies, cheese, etc)
For all other meals – either mix everything and take a small sample, or make a sample from each part of the meal. Be sure to select parts where cross contamination is likely to occur – such as cut lines on pizza, sides that touch a grill, etc.