The symptoms listed here is the best list I've seen. (For my dog, the first symptom was hyper-salivation, which then became drooling. Then she started to look uncomfortable.)http://www.globalspan.net/bloat.htm
The links at the bottom are very good and worth reading further.
I have this list printed up and hanging on the inside of a kitchen cupboard. I don't want to be logging on to my computer and hoping that my cable/broadband is working. I've also read it often enough to have most of the symptoms memorized. My dog started to bloat when I was nearly an hour away from home and approx 30 mintues away from my vet's office. Which leads me to the next issue.
We need to have Extra strength Gas-X (or similar) with us ALWAYS. Carry it in your car, your briefcase, your purse, your training bag. Have a bunch of it at home. Don't use it for yourself, or if you do, buy some for the dog and some for you, and mark it appropropriately. When you run out of yours, go buy some. I know someone who needed Gas-X for her dog, but she used up her stash here and there; didn't have it when she needed it; then had to rush out and get some (fortunately, it turned out ok). Don't steal your dog's Gas-X! Your gas pains are uncomfortable. His could be deadly!
When my dog started to bloat (I wasn't sure, but I suspected), I had foil packets in my car and my bag. I gave her two (pinched off the end and squeezed the medicine down her throat), called my vet to tell her I was on the way, got halfway there, pulled over and gave my dog two more. I had plenty of Gas-X to buy us time.
Simethicone is a rather harmless drug, all things considered. For a 60 lb GSD, I'd start with 2 capsules; for an 80 lb GSD, I personally would give 3-4 depending on the severity of symptoms. Ask your vet NOW what she thinks the dosage should be for YOUR dog. It may vary depending on age, health, proximity of vet or emergency clinic, etc. I'm not a vet. I can only tell you what I would do.
You should know where at least two emergency clinics are. Have their phone numbers stored in your cell phone or posted near your land line and in your car (carry business cards in your wallet or glove box). Call ahead. If the staff is already involved in other traumas, they may not be able to take your dog. If your dog is experiencing torsion and the surgeons are involved in a complicated surgery, they may not be able to take your dog. Be sure you tell them exactly what symptoms your dog is having and that you suspect bloat. Ask if they can treat your dog asap. If not, move on to your second choice.
If you can't get to the vet asap -- if you are delayed for any reason (or if you get there and they can't take him right away) -- and it doesn't appear that your dog is experiencing torsion yet -- you can try to walk your dog briskly. Don't let him run, no matter how panicked he seems to be, but this isn't the time for a stroll, or stopping and sniffing. Moving quickly can help move gas out of the stomach. It's one of the things that vets do to help horses with colic. Obviously, this is not your first line of defense. Your first line of defense is to get to an emergency clinic asap and insist that they treat him immediately.
Above all, stay calm. If you panic, you'll stress your dog. Create a plan now. Talk to your regular vet. Can she handle an emergency GDV situation? Can she handle it at any time (including closing time, weekends, etc)? Will your dog have overnight monitoring there? If not, an emergency or critical care clinic may be a better option for you. Ask her (or friends) for recommendations now. Print that information up and put it in several places. Give it to pet sitters, family members, etc.
When GDV happens, it happens fast, usually with little or no warning. It can happen when you're away from home (as I found out). The more we prepare now, the better we'll be able to respond. And what our dogs need most in a medical emergency -- especially one as painful as GDV -- is a calm reassuring owner.