Many good suggestions above!
My opinion is to go to sporting good store like Walmart and buy an inflatable boat big enough for everyone in your family. Self-inflating is better. Make sure it has paddles in the box. Leave it in the attic for the next big flood. Make sure you have a way to escape from the attic to the outside (i.e. fire-ax or an exterior door). Store non-perishable food items (cans, military MREs, etc), general first-aid kit with alcohol, and dry clothing, towels, and blankets up there too. Try and find one of those new "swamp straw" filters that you can safely drink polluted water through or store sealed plastic bottles of fresh spring water up there - Desert Climate: 1 gallon per person per day depending on the climate. Put a battery operated or hand-crank AM/FM radio and a fully charged up cellphone (any kind) so you can call 911 on it. You can use an old working piece of crap cellphone as you don't need to pay for service to call 911 or the operator these days. Just keep it fully charged up though!
Know your GPS coordinates (latitude and longitude) for the authorities. During a flood sometimes streets and signs are totally covered by water and debris and federal (FEMA) authorities don't have clue where 123 Main Street is during a flood - no landmarks visible. However a GPS coordinate and a good description of your house is better. Also mount a portable flag on the roof like a bright-red flag with your family name and tell them to look for it. Ask your buddy with the new GPS unit in his brand-new SUV to come over to your house tomorrow to give you your GPS coordinates. Write them down and save it in a safe place upstairs (on the back of the cell phone?).
Never try to swim out or walk out in a flood. Its either under heavy water current (even 6 inches of water!), contaminated with every filth you can imagine, full of live wires, full of dangerous & very annoyed critters, ground washed away, or you will drown. So stay put until the help arrives. Going to high ground is not an option when the water is ALREADY up to your living room couch!
Invest in a battery operated C.B. 2-way radio and call for help on emergency channel 9 (not the more popular & worthless FRS or GMRS radios!). Walmart and Radio Shack sell them. Keep LOTS of fresh AAA, AA, D, and C cell ALKALINE ONLY batteries on hand. Don't waste batteries by just listening to your CB, TV, or radio. Turn it off until you're ready to calmly call for help or listen to emergency news. Take a big magic marker and write a sign or on your front door PEOPLE ALIVE INSIDE UP IN THE ATTIC and include the date and time too just in case that's not true anymore the next day.
Don't have any 'loaded' weapons around you as you might shoot a first responder trying to break down your locked or blocked door. No bad guys are going to attack you today during a flood. They are trying to save their butts too. But be ready to scream outside or wave bright objects for HELP every time you hear people, a boat, helicopter, or truck pass by.
NEVER use your emergency flashlights unless you ABSOLUTELY need it. Save that battery power as you'll need it in the middle of the dark moonless night when you hear a stray dog, raccoon, skunk or possum trying to climb up on your roof during the flood. Learn to eat and do other stuff in the dark - get familiar with your attic's lightless layout today. Also get yourself one of those emergency chemical camper toilets (and TP too) unless you want folks smelling up your attic when they gotta' go. Boys have to sit down sometimes too ya' know. Go to Walmart again...
Don't assume you have flood insurance! if you didn't ask your insurance agent for it then YOU DON'T HAVE IT! Don't expect FEMA to help either. If you live in a flood prone area spend the extra money to get FULL coverage!! You'll wish you had after its all over. Make sure your important papers are stored in a fireproof lockbox in the attic or the top floor.
Oh and if you buy one of those $200-400 gasoline AC power generators from Pep Boys, Lowes, Home Depot, etc? Make sure you get a carpenter to build a moderately high-enough exterior flood shelf out back to mount it on. You will need to chain padlock it too to stop your neighbor(s) from BORROWING it during the power outage (i.e. "oh I thought they abandoned it..."). Do NOT run this thing in your garage, attic, or anywhere INSIDE your home or you will kill your entire family with carbon monoxide poisoning!
Remember to take your PETS with you! You tell your 1st responder its a seeing eye cat or dog or anything to protect your loved pet. Have its carrier, food tray, food, and litter box handy up in the attic. Nothing worse than post-flood stray animals looking for their masters dying or near death WEEKS later!
Hope this helps...
Hurricane Katrina and Rita
"Good job Brownie!" - President Bush