It's as simple as this: there is no reason to ever buy pre-made guacamole. Unless you're in a Mexican restaurant. Or if you're in a place that has no avocados for sale. (Like the corner store.)
In this modern day, there are almost avocados for sale, and for most of us, they aren't exactly local anyway. So regardless of the amount of time or ingredients you have on hand, there's no excuse to buy guacamole in a jar or even a locally-made container. At a minimum, all you need is a knife, a fork, a bowl and some salt.
First, pick out your avocados. You want them to be soft, but not extremely soft (or they'll probably have started to turn). Hard avocados will need to sit for a few days to ripen. Colour matters less than feel, though generally, they get darker as they get riper. Give them a gentle squeeze and you'll be able to tell how soft they are.
Slice the avocado in half around the put and separate. The pit will stay attached to one half. If there's no brown mixed in with the green (and no audience to watch your primitive method), squeeze the avocado out of the shell and into the bowl. You can also use a spoon to achieve the same result more gracefully. Pop the pit out of the other side, then add scoop the rest of the avocado into the bowl.
For the quickest guacamole, take a fork and mash the avocado, then add a good dash of salt and mix. That's it. We wouldn't serve this to guests, but for an afternoon snack for yourself, (or a quick topping for quesadillas), it's enough.
Mash, add salt and a spoonful of salsa, then mix. This decreases the visual appeal of the guacamole, which turns a bit brown because of the salsa, but it tastes better. We would serve this to a very good friend, and show off our salsa short-cut. Or just serve Bare-Bones Guacamole with salsa, and take a little of both as we go.
The Real Deal
Proper guacamole includes the following: salt, mashed garlic, diced onion, diced (and seeded) tomato, lime juice, finely chopped jalapeno peppers, finely chopping coriander (cilantro). If I'm making guacamole for friends, I'll made the real thing. But I'll sometimes skip the jalapenos, depending on who's going to be eating it, and I usually can't be bothered with the tomatoes. However, I won't overlook lime juice, onion and garlic.
Lime juice helps guacamole stay green, but it still doesn't keep for more than about an hour or two. And even then, it starts to brown. Which is another reason not to buy something in a jar. What on earth are they putting in it to keep it so green?