At the Port of entry, you need to present your Ugandan eVisa approval letter that has been printed out and passport, which must be at least 6-month valid by the time you enter Uganda. The barcode present in the approval letter will be used for accessing your application at the point of entry so bringing it printed will speed up the final approval process done.
Besides, it is highly recommended to bring along the Yellow Fever Card and a booking confirmation of flight ticket leaving Uganda.