With no idea of this packing list, I'm going to guess "tickets" means one of two things - either (a) the list has been in existence for a number of years, predating the virtual (but not complete) elimination of paper tickets in favor of e-tickets and refers to those paper tickets, putting it in the travel documents category; or (b) yes, it means park tickets and is applicable if you possess actual tickets before leaving home - because you don't want to forget those - putting them in the valuables category.
What categories, you ask? The four categories of items you should always pack in your carry-on luggage:
travel documents
medications/medical equipment
valuables (tickets, jewelry, electronics, etc)
whatever items you will need for the first 24 hours at your destination