One thing that raised beds require is a continual renewal of the soil in order to maintain its fertility. You can pull the old soil out and remix it, but that strikes me as something they call "work". I'm not in favor of that if it can be avoided.
There are also commercial fertilizers, such as the ubiquitous Miracle-Gro. Yes, they work, but they also cost money, and if "something happens", you may not be able to run down to the local big box retailer to get more. But it doesn't hurt to stock up on some in case of an emergency. They can get you through something like an unexpected need to ramp up production by 3 or 4x.
You can use animal manure, but that one you have to be careful with because of parasites and its chemical make up. I'm not going into the details, you can read this if you're interested in the whys and hows.
I'm more in favor of compost tea. There are two variants that I know of, brewed and steeped. (Yes, this sounds a lot like drinkable tea. Some people love to carry analogies a bit further than they should, but we're going to have to go with the flow.) Brewed compost tea requires external inputs such as molasses and air pumps and I'm not going into it here, because I'm looking for cheap, easy and available in a long term emergency. That leaves us with the steeped variety.
Basically, steeped compost tea is really like steeped tea you would drink, except you don't need to boil the water. Get a container, toss in some compost and water, then wait. Use the result to water and fertilize your garden. Eazy peazy.
In reality, it isn't that simple, because you need good compost, which isn't as easy to make as some people think it is. You're also going to make this in large quantities, so we're talking 55 gallon drums, lots of water to deal with, and some way of distributing it. Watering cans work, but if you're watering a lot, you might want a pump and hose, or better yet a gravity fed system if you can work one out.
Obviously, you can spend a lot more than 5 minutes on this, but here's a quick video that will let you dip your toe in the water. Don't do it with the tea, that stuff's yucky.