So I'm playing Castaway, and I eventually earn some quest items, such as the Beetle Shield and the Fire Scimitar. Unfortunately, in this game, there's no way to view the stats of an item, other than in the shop. How do I know how these items compare with the others in the shop?
Those stats in the shop aren't the items' actual stats. They're the stats relative to your current equipment's stats. So, all you have to do is equip the unique item that you want to compare and visit the Blacksmith to see how much better/worse every item sold is. There is a bug however that the stats in the shop won't know that you have stuff equipped right after loading your game until you enter an area and come back.
If you want to compare two quest-rewarded items, you can equip one, look at your stats and then equip the other one. (That's assuming that there are more than one item per equipment type. I'm only roughly 1/4 done with the game.)