Hi there,
Your story has to come from the heart. We are all trash lovers here, but we all still have our own preferences and dislikes.
If you are thinking of someone being shoved in a trash bag and having items thrown in, then consider your own preferences. These may either be things you’d like if you were being bagged yourself, or items you find could be a turn on if you were watching someone being bagged. If a particular item really doesn’t take your fancy, don’t use it. Try find the things that either you’d want yourself, or would enjoy watching land on a victim.
Trash comes in all sorts of form and sizes. You can have normal things like packaging, your generic stuff that isn’t overly disgusting. You can go with things containing bodily fluids such as condoms, female hygiene products, diapers. Some people love bringing food waste into it. Sometimes if it’s disposing of a particular person, their own belongings may be tossed away with them. Think about what gets you excited and gets you going. Some of my own stories had scenes I personally wouldn’t want to be in, but the idea of seeing a helpless female in that scenario excites me.
Go with your gut, go with your preferences, and the writing will flow. Our stories are our fantasies, and we can make them go the way we want them to!