If you are traveling to (or live in) the zone of totality, don't bother viewing the partial eclipse at all. It's not what you are there for. You are there to experience the total eclipse in all its glory, and you can't use eclipse glasses for that.
Your best viewing tool for the total eclipse is your own eyes and a good pair of binoculars. Yes, plain, unfiltered binoculars. During totality you can look directly at the solar corona. Not only do you not need eye protection, but you'll miss the whole thing if you use any kind of filter.
This is true only during totality, of course.
I recommend doing what hundreds of us did on an Oregon hillside in 1979. During the first partial phase, we put on sunglasses (just ordinary sunglasses) and looked away from the sun. The purpose of this was to get our eyes a bit dark-acclimated, so when it went total we would have an even better view.
By looking away from the sun, you also have a chance of seeing the other interesting effects on the ground: the wavy ripply patterns that appear just before totality, and the shadow of the moon as it rushes toward you at thousands of miles per hour!
As soon as the eclipse became total, people started yelling "totality!" and we took off our sunglasses, turned around, picked up our binoculars, and enjoyed the awesome experience of seeing the solar corona.
The only danger here is that you have to stop looking as soon as the first bit of the Diamond Ring or Baily's Beads appear. Then you're back into the partial eclipse and must use eye protection.
But at that point, most of us just cheered and got ready to go home. After totality, the partial eclipse is not much to get excited about.
If you're not in the zone of totality, then of course you must not look directly at the sun at any time. But if you don't have quality eclipse glasses, you still have some other good options.
One is a piece of #14 arc welder's glass. Another that you can improvise on the spot is a pinhole projector. There are various ways you can make one; at the simplest it can just be two pieces of paper, one that you punch a small hole in with a pin, and the other on the ground or a wall. Hold the paper with the hole so that the sunlight goes through it onto the other. You will get a nice image of the partially eclipsed sun projected onto the other paper.
A pinhole projector is the safest way to view the partial eclipse: you are never looking directly at the sun at all, only its projection.
There are numerous plans for building slightly more elaborate pinhole projectors. This page has some good tips:
http://www.skyandtelescope.com/astronomy-news/how-to-look-at...
Or search for "solar eclipse pinhole projector" to find more.
There is a lot of misinformation going around about eclipse viewing and eye safety. Everything above is true and correct to the best of my knowledge, speaking both from personal experience and extensive research. And I've tried to make very clear the difference between the partial and total eclipse. Of course, if I made a mistake or left anything unclear, please let me know!
There are two main dangers regarding eye safety. One is that someone may view the partial eclipse without proper eye protection and will destroy their vision. This has happened many times, and it is a real tragedy.
The other danger, albeit of a lesser sort, is that many people who travel to the total eclipse zone will mistakenly believe that they need some kind of eye protection during totality. As a result, they will completely miss the awesome, life-changing event they went to so much trouble to see.