No one can completely be prepared for a flood to happen. You can have the canned foods, the fist aid kit, dry clothing in ziplock bags, extra toiletry items in plastic bags, etc. The only way to completely prepare for a flood to happen is to buy home insurance, to protect your home and your belongings.
A flood can cause a lot of damage to the inside of your home. A lot of repairs will be needed. Those kinds of repairs would include fixing the drywall, the flooring, the furniture, electronics, etc. Not many people have the money laying around that it would take to completely fix the damage in their home. Many things would go unfixed, which could cause mold issues. That would be a bigger problem than you started out with.
This is the type of situation that making an insurance claim comes in handy. You can take pictures of the damage. Have someone come out and see the damage. Once the paperwork and the process are complete you will be able to fix your home to be livable again. All paid for by your insurance company. If you ever have any trouble getting money from your insurance company, remember a loss assessor can help you with a flood insurance claim and make sure you get a just amount.
Insurance may never have to be used, which is what you hope for. You never know what will happen though so it is better to be on the safe side.