Resources

I need not tell you how vital the production of Gold, iron and food are in this game. Troops have to be bought using gold and iron and maintained with food, just like the real world.

Much is said about upgrading catacombs to enable us to keep a proportion of our resources in the event of a raid and, for resources already claimed, this advice is sound. I'd like to mention the rewards that are given through daily logging in, from tournaments etc.
In my experience, these awards stay in place in the Black Market until you claim them and I tend to use this storage facility like a bank.

Don't leave the rewards from League Quests at the Black Market - they only remain available to you for 3 days before they vanish . Most other awards will sit there until you claim them, so it makes sense to leave them where they cannot be taken by raiders and draw them as and when you need them.
So, my advice is - catacombs for keeping what you've already made or claimed, but use the Black Market like a bank for other awarded resources.