This is likely Piers Anthony's Dragon's Gold, first book of the Kelvin of Rud series.
The Prophecy: A Roundear there Shall Surely be; Born to be Strong, Raised to be Free; Fighting Dragons in his Youth; Leading Armies, Nothing Loth; Ridding his Country of a Sore; Joining Two, then uniting Four; Until from Seven there be One; Only then will his Task be Done. When Kelvin was a child, his mother read to him from the Book of Prophecy and he asked what the poem meant. Now he was about to learn. The Kingdom of Rud languishes under the heel of a usurper; an evil sorcerer has taken the throne in the name of his wicked daughter. Even deep in the forest, away from all power, the people tremble and await the day of prophecy's fulfillment. It cannot come too soon: Charlain and her children are soon to lose their home to the tax collector. But Kelvin and Jon have other plans. they have found a dragon's territory, where scales of purest gold, shed by the dragon, lie free on the ground for anyone with courage, or innocence, to take. And the words of Mouvar the prophet echo across Rud.
The berries in question are poisonous to most, but Kelvin, as a "Round Ear", instead gets the OOBE experience when he eats them as a slave, trying to escape his drudgery. Not long after, he acquires a set of gauntlets, I think from the crook of a lightning struck tree, which are very durable and insulative, but he also uses them for the mundane act of cracking nuts. He finds another Round Ear, Heln, who can also do the OOBE thing with the berries.
It was followed by four sequels, Serpent's Silver, Chimaera's Copper, Orc's Opal, and Mouvar's Magic that follow the adventures of Kelvin and his family across multiple worlds of varying magic and technology.