Branded promotional products are like free advertising. What you do is pick things that are interesting to your customer base. If you sell an exercise or nutritional product, things like high quality water bottles are popular. If you sell parts or tools, tiny flashlights and pocket tools are popular if they are made well. Maybe your business would do best just offering a nice magnet for a refrigerator. There is something for every business type. Just be sure to pick something that is of superior quality. You do not want your customers associating your business with an inferior promo product.
The good thing is that you can get customers to buy your promo products if they are made well.