When I bring down gifts, for some staff memebers, the gifts are a instead or a suplement to their CUC tip. I try to bring down worthwhile items that cost me very little compared to their value. For example, sanitary napkins, Stayfree 18 ct, I purchased for $0.37. So if I was to say tip 1 CUC or the sanitary napkins, I’m sure the waitress/maid/cleaner would be happier to receive the napkins. At least I would hope so. Another example, I purchased childrens vitamins at costco, who indroduced new packaging so the old packaging were on sale for $6.99 for 2 bottles of 120 pills each. That means that it is costing me say 3 CUC for a bottle of childrens’ vitamins. When I befriend the staff and know who has children, I’m again pretty sure, they would prefer the childrens vitams to 3 CUC’s.
So to answer your question of what they prefer, my impression is that if they are worthwhile gifts they are more valuable than CUC. I’m sure the black market will allow them to sell/trade whatever they don’t need, and this will bring in more CUC then the equivalant cost to me.