Still planning the environment system out, which leads to the next change in Nostalgia's game mechanics: your items are affected by the evironment!
I got the idea while I was playing Lunar Knights, because your perishables items (meat, fruit) spoils if not used in a certain amount of time.
So I came up with this plan:
Jerky
Pork
Steak
Pork and Steak spoil after a few days (in game), turning them into Spoiled Meat, which harms you instead of healing you.
However, to prevent this, you can have your Pork and Steak cured in a town to prevent them from spoiling. Jerky won't ever spoil, since it was prepared that way.
Water
Spring Water
Liquid Ether
In snowy weather, if you stay out long enough, your Water and Spring Water will freeze, halving their effects. Liquid Ether is unaffected by the weather.
Holy Arcana
Tent
The Holy Arcana revives a fallen ally. However, if you spend too much time in the rain, the Arcana becomes soaked, and will only restore your ally to 1 HP instead of 1/4 their total HP.
Tent provides shelter for you, restoring your HP and MP in the field. But as you wander in the plains, or high in the mountains, you might run into a thunderstorm. If you are struck by lightning, you'll take damage, and there's a chance one of your Tents will be charred, causing it to randomly either heal a small bit of HP, a small bit of MP, or do nothing.
To accommodate for the items being affected by the weather, and therefore possibly changing types on the fly, your inventory will be limited to 64 item slots, each slot holding one item. It's not unlike Illusiat 13's iventory, but it only holds items. Key items and equipment are held elsewhere, as they don't need to change on the fly.