This is the 6085th most frequent Russian word.
списка
"Spiska" (списка) is the genitive singular or nominative plural form of "список," meaning "list."
The word 'списка' (genitive form of список) is used here to indicate possession belonging to 'shopping' (покупок), forming a meaning of 'list of shopping items'.
Я нашёл свой старый список покупок.
I found my old shopping list.
The word 'списка' appears in its genitive case form to imply the item belonging to the list (список), showing its position within it.
На вершине списка был самый важный пункт.
At the top of the list was the most important item.
The word 'списка' is used in the genitive case indicating the source — ‘from the list of tasks’.