All items to buy in the shop should be social in nature. If your use/existence of the item doesn't affect other members, then you should just have the item as a default feature.
Buy stickies of varying strength
Buy message icons
Buy profile backgrounds to fill in the blue space
Buy profile themes that give the entire profile a custom feel
Buy bulk likes/super like. Has ten times the power of a regular like.
Buy change custom title
Buy change someone else's title
Buy steal credits
Buy mod immunity (joke product at super expense)
Credits
KASS
1 credit per wall comment, 2 credits per post, and 3 credits per topic. A wall comment like gives you 1 credit. A post like gives you 2. A topic like gives you 3. Someone liking your profile gives you 5 credits.
Topics give the OP bonus credits upon reaching milestones. Every 10 responses gives 2 credits, up to 500 responses. Thus a total of 100 bonus credits can be earned from topics.
Edited by the bot
Each item should be a real and specific entity.
Make a table for all items. Include current owner, item info, and ownership+price history. Allows for future expansion and makes it simpler for me I feel. Shipmints come in every Sunday and are the main source of new items into the table. Members may also directly recieve items by performing certain tasks and reaching milestones. These items are generated upon being given to the member.
Track money by the hour for users individually.