Predict items customers would buy in next order
Try association rules, they will help you in finding the right set of rules like what is chance of customer buying X if he purchased A, B, C in the past.

Also from my personal experience, these kinds of tasks are more business need driven. Like sales capture from the item. So even if your model is 60% accurate but captures 90% sales, you should be good to go. Try to give it a thought in this way.