3M Cavit Temporary Filling

In short, this is the best industry standard for a temporary filling if a tooth breaks when out and about. This may not be ideal for many (I'm a WFR and backcountry guide), but this is always in my 1st Aid Kit that goes everywhere I go.

This is a necessary part of a kit if you are a care provider in the backcountry. This stuff comes out of the tube like a putty, and is very easy to work with. Simply roll the product into a ball after prepping/cleaning, and press into the broken area. It is not necessary to fill the entire void, pressing it in will make an appropriate seal protecting the nerve. After placing, simply bite down to finish molding the filling to prevent additional damage to adjacent/upper/lower teeth.  

The product is designed to cure/harden when moist, an obvious necessity. A plus with the design is that the material slightly expands to create a good seal, and to stay in place until one can get to a professional. The material will set pretty fast (<1 hour), but it is not recommended to eat for several hours.

One note is that you will want to replace this stuff every couple of years. It tends to dry out/harden when exposed to the typical high/low temperatures of backcountry travel.