These are occasionally released offers that start on thursdays and go on for a week. There are 5 tiers with incremental gem costs and offer varying amount of food, green rings and equipments. There are 5 types of offers and you can change the one offered to you by contacting official support.
To change your offer, visit the support page here or using the in-game button to contact support. Scroll down on that page and choose "Payments" category, "Change Offer Price" sub-option and tell them the type you want from the types below.
Select your region and view all types to see what they offer, and choose whichever you feel is the best.