Plan on going to the Amazon.. what if you're bitten by a snake in the middle of the rainforest? Do guides have anti venom or do you die?

There are some beautiful pit vipers in the Amazon. If you watch where you put your hands and feet, you are unlikely to be bitten though. Remember the American slogan: "Don't tread on me." So many snake bites result from stepping on a snake, and you can't blame the snake for that!
The guides should carry a good snake bite kit; I suppose you could carry one of your own.

Antivenin only works for one kind of snake, often only 1 species of snake.Different kinds of snakes have different kinds of venom. Cobras and coral snakes have mostly venom that attack the nervous system. Rattlers and viper venom usually attacks muscles and the blood. Therefore it would not be possible to both carry all the difference kinds of antivenin and be able to figure out which one is needed to cure the victim. The chance of dying is real, not just in a foreign country when bitten by a venomous snake, but also in the USA, where antivenin is more readily available. Getting to the hospital quickly before the venom kills is the key to survival.

Luckily, it is pretty unlikely that anyone will encounter a snake, as most of them hide instead of being out in the open most of the time. Even professional scientists who are snake experts may not see any snake after a whole day looking for them in the wild. The best way to avoid being bitten is to be careful where you put your hands and feet, and wear long thick heavy denim jeans and snake proof boots.

Carry with you a good snake bite kit the kind with a high vacuum hand pump. Nobody carries around Anti-Venom it's quite expensive. And stay alert. wear protective clothing you know you're going to a dangerous place! The best antivenom is not to get bit

You won't die if they remembered it

That would all depend on your choice of guide. For a dollar, you could get Fred Bloggs to take you and he would carry a pointed stick and a dock leaf incase you got stung by a nettle. If you pay for a decent guide, he/they would carry all kinds of medicine and he would have first aid training so would know how to administer it.

depends on if it is venomous or not

An awful rare happening, and so few dangerously venomous snakes and animals.
Usually such expeditions are equipped with satellite phone they could cal for airlift in event of injury