you would Buy because Thing. Person does not want (to) Thing. Person does not want (to) Slip. 
Meal is related to Pig. Pig is related to Small. Small is related to Can. you are likely to find Can in/at/on Trash. 
Buy --MotivatedByGoal--> Thing <--NotDesires-- Person --NotDesires--> Slip 
Meal <--RelatedTo--> Pig <--RelatedTo--> Small <--RelatedTo--> Can --AtLocation--> Trash 