When you pick up a certain item you can have it run any command you want.
Config looks like this:

command-executed: "/say pickup"
item-type: "TOTEM_OF_UNDYING"
remove-item: true

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Change "command-executed" to change the command you would like to execute
Change "item-type" to any item material type in all caps (Cap sensitive) to change the item the executes the command
Change "remove-item" to decide whether or not it will remove the item when the command is executed.