I have it down to a science (for me, that is). I bring one rolling tote and one tool caddy. One trip in, one trip out.
If I'm going to a lss, I will just bring my tools, my container of brads/eyelets/flowers, and photos. I will buy everything else at the store. The last time I did this I got 7 layouts done and spent $20.
If I'm not at an lss, I will also bring a stack of cardstock, coordinating patterned papers and embellies that I pick out ahead of time to go with my photos. My fav thing to do is work on themed albums or projects. It makes the packing easier.
I also don't fret about leaving anything at home. I can always add finishing touches at home.
As for drinks....I once saw a woman knock a large coffee all over another woman's layouts, photos, everything. So much was ruined!