Part 1: Bugging In
In Austin, Texas, as with any city remotely heavily populated, staying in your home is a bad idea unless you have a bomb-shelter already in place. Windows and doors take too much of your valuable time and resources to reinforce, and you likely don't have mass stores of food and water already put aside (unless you stocked up during the Y2K scare).

Your best bet is to quickly (but smartly) gather any necessary medical supplies and long-lasting food items into the largest bag you can carry without sacrificing too much land speed (and not so strapped-on that it would be difficult to ditch in a rough spot).

Make calls to as many friends you have that are most likely to survive and won't drag you down - though having the one person in the group who is slow could come in handy in a pinch (you don't have to be faster than the zombies, just faster than that guy). It's heartless, it's cruel, but you can cry and atone later - at this point, it's Darwinism at its finest. Have your survivor friends (the ones that can be reached) attempt to converge at a predetermined rendezvous point.

Have the plans at the ready to proceed to Part 2 as quickly as possible.

Part 2: Bugging Out
Get in your car and drive.

It may be best to learn a bit of auto theft technique in case you have car troubles (ie: a collision with a zombie, flagpole, etc. takes out your radiator or engine; your car has been stolen - irony; a faster or better defended vehicle has been found; you run out of gas, etc).

It is best to have a mapped route to your BOL that does NOT involve any major roads or highways, as these are likely to be packed with evacuees and therefore potential zombie masses. Should Z-Day begin at night, it may be best to drive primarily through commercial or industrial areas as most people - and potentially, zombies - will be in their homes, and vice versa during daytime hours. It is advised to have a plan for both scenarios.

Part 3: Digging In
Your BOL, and new home away from home is to be the nearest Sam's Club (or Walmart if there is no Sam's nearby). Other warehouse stores with ample grocery sections would also be usable.

Here are the perks:
--Plentiful and large - for easy access and maximum survivor housing
--Few entrances and exits - for easy defense and monitoring
--Large, flat roofs with high visibility from the air - assuming military assistance hasn't also fallen
--Massive stocks of food - eat the perishables first, it may be the last pizza or toaster struedel you ever have.
--Large shelving units - makeshift 'tree houses' to house more people, and provide escape routes in the event of a zombie break-in
--Pharmacy - likely stoked with many painkillers, vitamins and antibiotics to help keep you at your best (hell, maybe even to celebrate with a bit of recreational use, why not?)
--Sporting goods department - depending on your region, this is likely to house guns, ammo and other weaponry and camping equipment handy in the event of the need for escape or defense
--Massive amounts of propane and cleaning chemicals - to use as bombs, molotov cocktails, and other weapons (prepare these immediately after the building is secured and any ill or injured are seen to)

Using fork and scissor lifts (which are plentiful in any active warehouse), move the largest and heaviest pallets of non-essentials (electronics, furniture, gardening supplies, ect. - pet food technically is a potential resource, gross but true) to block all entrances and exits - except for one. Any true survivor knows there always has to be a Plan B. Park a fork/scissor lift (with key still in the ignition) in front of one of the doors so that in the event of needing a quick escape, it can be easily moved and the door can be freed.

Part 4: Living
Living would be fairly simple, though to a point of being remarkably primitive. Once perishables have expired, they should be thrown as far from the building as possible (via the roof) to prevent your new home from reeking of it. Clothing and other fabric items can either be used as wardrobes or used as torches and bandages when regular supplies run low.

It is during this time in your safe house that you should re-vamp your fitness routine: jog laps regularly, lift weighted objects and hang ropes to climb. Just because you made it this far, doesn't guarantee you'll go any farther. Watch your diet and maintain a diet high in proteins until supplies run out - this will help reduce body fat, and gain muscle, and them move to high carb - this will use your supplies of pastas and breads plus give you continued energy to maintain your fitness regimen.

There should be a minimum of two monitors on the roof at all times - preferably with guns and decent aim. One will monitor the North, the other the South, rotating on East and West as needed. They will have the following duties:
--warning the others inside of an approaching zombie herd
--maintaining a signal or sign for aerial rescue
--flagging down other potential survivors to the site (this duty is not likely to be long-lived, pardon the pun)

Inside, there should be someone on duty at all times to monitor any health conditions amongst survivors (whoever has the most medical experience should have this position, obviously). Also, a rotational check of the barricades, weapon stock, and food supplies should be maintained. Regular rationing and inventory should be kept to make sure the resources available stretch as long as possible.

Likely, there should be an 18-wheeler still in or near the loading bay. Check it (or better yet, them) for fuel supply and pre-stock with a supply of medical items, non-perishables, and water. Depending on fuel supply, try to map out the broadest radius of potential travel distance to locate the next safest location within reach. This will be optimal for when other supplies run dangerously low, or a quick escape is needed so that you and any other potential survivors can find a new safe location.

Part 5: Cold hard reality and your inevitable death.

Once you reach your Wal-Mart that you intent to convert into a fortress you will see the hoards of unprepared attempting to do the exact same things laid out in this plan. The store will be a killing feild as half crazed people beat eachother to death with their bare hands for the last battered pack of chewing gum. You will be over run by the hoard and slowly left to rot where you fall as your corpse is picked clean by the gathering mass of terrifed consumers. This plan is a death trap do not use under any circumstances unless you are hopelessly suicidal.