Down in New Orleans they have two kinds of trinities - the church trinity and the cooking trinity. The cooking "Trinity" is composed of close to equal parts onion, bell pepper and celery. It is also the base of practically every New Orleans' dish imaginable, including jambalaya, beans and rice, gumbo and etoufee.
Cut the top off the bell pepper and then remove the core and the seeds. You may rinse under water to get all the seeds out. Then chop the peppers into very fine pieces.
Peel the yellow onions. Chop them into fine pieces, too.
Chop the tops and the wide, whiter-colored base off the celery sticks. Then chop the celery into small pieces.
Add all the chopped ingredients into the gallon-size freezer bag. Then give it a good shake to mix up the ingredients.
Place sealed bag into the freezer.