"shop till you drop" a figurative expression meant to say "shop until you are too tired to shop anymore". Simply put, drop = collapse out of fatigue. This phrase has sort of become a catchphrase in some stores that boast a wide variety of products, mainly due to the phonetic ring to it, as 'shop' and 'drop' rhyme.

I can take you to shop until you drop= I can take you shopping until you are too tired to stand up.