3) Most divers apply some form of anti-fog coating before each dive. Spit works for some people, I don't find it to work especially well, maybe my saliva is different. Some people use diluted baby shampoo which works ok but is a hassle to carry around.
Totally agree on spit. Works okay for me, but not great. Works great for some people. Doesn't work at all for others.
I don't know why it would be any more hassle to carry some baby shampoo than a thing of commercial anti-fog. And I DO know that I have used commercial stuff before and failed to rinse my mask well enough and gone through a dive with that stuff stinging the crap out of my eyes.
I use this exact squeeze bottle for my diluted baby shampoo:
Amazon.com: Under Armour Undeniable Squeeze Bottle with Quick Shot Lid, Clear, 32 Ounce: Kitchen & Dining
I like it because it holds enough that I only have to refill it every few dive weekends. And the lid twists to lock closed so it doesn't accidentally squirt baby shampoo into my bag. It's kind of soft, so it's easy to squeeze. And it's tough, handling being thrown across a parking lot, for example, hitting the ground, and still being fine.
But, if you don't want something that big, you could definitely get a travel-sized shampoo bottle to put it in and it wouldn't be any bigger or more trouble than a small bottle of commercial anti-fog.
The only reason I carry around such a big bottle of it is that I also use it (liberally) as suit lube, so I go through it a lot faster than if I only used it as anti-fog.