I have 2 different ways to do it depending on my goal,
1. I have no goal other than to Cache. I load all the caches that I have in gsak to my map software and look to see where the most or most interesting caches that I find for they day and buuild the rout there to get what I want in the most efficent way I see. After I get the route figured out a use Gsak to filter down to the ones in the general direction I was to go and load that and the route to the GPS.
2. If I my purpose is to go somewhere or at least in a general direction I still load the caches from gsak into my map software and them set the sart and finish of the route. After that I pick the route based on what caches are on the way and other personal preferences and filter Gsak to give me the caches that would cover that route and load the route and caches into my GPS.
But this is leveraging Gsaks features to keep cache reccords up to date and pq to send me all the caches in maine and border areas of NH and CA. I generally have about 4000 caches in gsak at any time.
later this month I am going to play with sites caches along a route feature for a trip out of state as I need to download all the caches between here and PA in a pretty wide swatch.
But for what it is worth that is my approach let me know if you need the details on how as I only gave the 40k foot view on that.