The Google Flights date grid is the single most useful flight search feature for budget travelers and most people aren't using it correctly.

The basic use: go to Google Flights, enter your origin and destination, then click 'Date grid' instead of entering specific dates. You'll see a matrix of prices for every combination of departure and return date. The cheapest combinations turn green. This alone can save you hundreds if you have flexibility of even 2-3 days.

The explore feature: if you go to the 'Explore' view and enter just your origin, Google Flights shows you a world map with prices to various destinations. Set a budget filter and a date range and it shows you everywhere you can go for that price. This is how I find my next destination — start with the price I'm willing to pay, see where it takes me.

The price tracking: hit the bell icon on any search to get email alerts when prices change. Set this up for 3-4 potential destination pairs, go on with your life, and let the deals come to you. I've saved $200-400 per trip this way.

The alert for error fares: Scott's Cheap Flights and Secret Flying are still the best sources for actual error fares because they have humans monitoring and flagging them. But Google Flights alerts are useful for general price drops on regular routes.