There are times that you'll need to see at a distance. While you could use a telescope, telescopes are generally something less than portable. Of course, if you are setting up a a fixed observation post, a telescope might be a good item to have to really get a good look a something. If you happen to be a dedicated gunnie and you own a spotting scope (or two, or three), you have this one covered.
Most of the time, you're going to be moving and need to see something in the distance. This is where binoculars come into play. There are a ton of different brands and more features than you might believe. Prices range from something like $20 into the $thousands, and for the most part, you do get what you pay for. For a good, quick read on what those features are, WikiHow has an article you can peruse. If you want to blow off the "5 Minute" thing, the Audubon Society has a current buying guide. Short version is that the best values are $300-$500, but there are good, useful binoculars available under $200. There is also buying used, but you had better know what you're about buying used optics of any sort.
A special case is the monocular. This is something I'd consider for a bug out or get home bag in order to save weight and space--if you buy the right one. Once again, WikiHow has a good what to look for article. There isn't a decent buying guide I'd trust that I can find.
Personally, in this situation I'd go for one of the inexpensive, low power binoculars in this case. They'll be small enough and give you a decent enough view for the situations you're likely to run into.
Don't forget to cover this area in your preps. You'd be surprised how many don't.