Q: Over the centuries, how have priests managed to obtain the bread and wine needed to celebrate Mass in remote areas? I have always wondered about that.
A: Because priests of the Latin-rite Church use unleavened bread, it is fairly easy for them to keep it for longer periods than if it contained yeast. Priests of the Eastern Catholic Churches use leavened bread that can be made where the Mass is celebrated.
Grape wine is sometimes more challenging to obtain and to transport, but it can be done. Not all climates are suitable for growing grapes, but wine can be imported from places where grapes are grown.