In my fantasy world there exists a nomadic people known as the Ròda. The Ròda believe in the collection of knowledge, lore, and more importantly spells. They practice their beliefs by travelling in small groups with each commonly having a large wagon. They then travel from village to village and city to city actively seeking out knowledge. This has led to the Ròda being labeled as "grave robbers" and "thieves" by the mage families due to the Ròda gathering any knowledge they can: digging through ruins, eavesdropping, etc.
However they are only allowed to write down this knowledge during a full moon. This is due to the "Moon Runes" the Ròda write their tomes in (mainly to avoid thievery. Who wants to steal a empty book?) This means that at times the Ròda will have a book's worth of information they must keep in their heads. Due to how magic works in this world they'd also have to be precise when they write them down.
What strategies could the Ròda use to improve their memory? Would any substances known to a medieval society help?
they can't jot down notes, that's heresy and can be found defeating the purpose of writing the tomes in moon tunes.
technology is the medevial high period. However the Alchemy would stretch into early renaissance.
spells have to be remembered basically word for word if you want to have predictable results.