All investigators have 2 hands . If the 1-hand slot is occupied and the 2-hand slot is free, it should be possible to use the 2-hand slot for a 1-hand item.If a 2-hand item is played, of cause one of the 1-hand items must be discarded.
Hence Roland should be able to have his .45 in one hand and his magnifying glass in the other., but if he plays his shotgun one of the two other items must be discarded.
I know that this is not exactly what the rules says, but that is the way I play when I play solo.