Timber, I'm certain others will offer ideas for up-to-the-ultimate in range loading for this, but I will offer my simple-man's version.
I learned, long before the internet about the basics of breechseating in some long forgotten book or article. Nobody hereabout did it at all, so I was on my own. I did have a rifle, and it came with a push seater- hence my interest. So, I loaded cases at home, where I could be as fussy as I liked. No need to prime and reload at the range. This, of course, won't allow one to adjust if desired. But, once I found a load that I could count on, I just took some of that one-for control, and various groups of others to compare. There were a few missteps, and plenty of learning got done, but me and that same rifle still are together. 
I still do it that way when I go to the range, with a box of cases plugged with removable foam pieces to prevent spilling. Earplugs would work, but there's lots of free foam to cut up. The only thing that has changed much for me is that old push seater recently lost its job to a new Weber seater I bought from one of the guys here on the forum. Good shootin', and don't forget to piddle a bit with fixed loads as well- I have pretty good results that way too.

I'm also new to breech seating, as I just began last year. I started out priming 50 cases, and charging them. Then shot them that way, until I ran out.
Later I got a Harrell's powder measure, and found it so accurate I didn't need to prime cases ahead of time. Or charge them ahead of time. I now use a Pope style re-decapper to remove primers and prime the cases. Then charge them with my Harrell's measure just before chambering them. Slightly slower pace when shooting, but I like it even better.

First of all for the cases get yourself a Re & Decapper, CPA Makes a good one that is comfortable and gives good control for seating. After a little use you will be able to seat primers better than any press with your Re & De. 
As far as powder goes bring your powder measure to the range. Set it for the load you want and drop it in to the case. I use a Harrell measure but any measure will do if you put in the time to teach yourself how to drop a consistent measure of powder.
If you want to see how I do it Google schuetzen rifle and look for a YouTube video. In it there is a close up of how I load from the bench. I haven’t changed my basic loading practice in years.

40 Rod

I use a re-de capper that Buffalo Arms used to sell.  Powder charges are pre-weighed at home and stored in glass vials that I also bought at Buffalo Arms

Pre-weighing charges may not be the best way, as it prevents you from making changes at the range.

Chris.

Rather than mess with separate vials, or corks for cases; I simple added some soft foam to the lid of my cartridge box. Glued it inside the lid so when I closed the lid it sealed off the mouth of the cases, and kept powder in them.

Another option is to pre-charge the cases at home, then pick up a small block of floral foam and using a knife, slice off a 1/8" sheet. Simply press the mouth of the case into it after charging and you will have a perfect plug that does not have to be removed before shooting.

Just be aware of the fact if using the foam approch depending on how far you have to drive they will typicaly migrate down towards the bottom of the case and not remain at the mouth and if not all the same amount neither will it be the results be at the target.