Bundle Past Purchases with New Products
When customers acquire one item in a bundle, they're motivated to acquire the remaining items.

Overview
Progress feels motivating.
In a popular study, customers felt motivated to collect loyalty points for a coffee shop when they started with 2 points already in place (Kivetz, Urminsky, & Zheng, 2006).

A new study applied this effect in ecommerce (Bauer, Spangenberg, Spangenberg, & Herrmann, 2022).
Customers bought more wine if they saw empty placeholders for other wines in a full-course meal (e.g., starter, main course, digestion).

Collecting a single wine motivated them to collect the remaining wines.
You could also implement this strategy after a purchase. Suppose that a customer buys a shirt. In their account, you could bundle this shirt with other products — such as a "casual night out" bundle of clothes.

By grouping past purchases with new products, you endow customers with progress. Since they collected one item in this bundle, they'll be motivated to collect the remaining items.
Anyone try this strategy? I've never seen it, but it seems like it would be effective.
Other New Studies
- Michelin Star? More Negative Reviews - When restaurants are awarded a prestigious Michelin star, their reviews get worse. Why? Because it creates unrealistically high expectations (Rita, Vong, Pinheiro, & Mimoso, 2023).
- Which Products to Recommend: Relevant or Profitable? - Businesses generate more revenue when they suggest relevant products, rather than top selling products (Donnelly, Kanodia, & Morozov, 2023).
- Launch Products During a Recession - Based on data for 10k+ product launches, products perform better when they're launched during a recession (especially in the later stages; Talay, Pauwels, & Seggie, 2023).