This is one of those tweaks I need to add, but have just never gotten around to doing. It wouldn't be too hard to do the wine/ale part, but I don't know that the salt and spices would be doable as a tweak. It was possible in vanilla M&B due to the order the items were listed in, but the item order is different in Warband. It's setup in such a way that making salt/spice behave as food would cause every other trade item to also behave as food (iron, tools, pottery, etc). That may make for some comical situations in game, but wouldn't really make any sense

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It would be very easy to do the salt/spice part via the module system, but not so much as a tweak.