It all depends on the purpose and how much beer I am bringing. If I am just going to brew club and bringing a beer for them to sample for feedback and to share, I just use a stainless double walled growlers. I have multiple 32oz and 64 oz versions, along with other single walled growlers too.
If I am bringing more beer for an event (when we were in our 20's and our friends were all getting married, they asked me to brew beer for their receptions), I bring my kegs, 20# CO2 tanks and jockey boxes. I have three jockey boxes, a 2 pass, 5 pass, and 6 pass, so I bring one or up to all three depending on how much beer I'm bringing.
When I got married, I even borrowed jockey boxes from a couple other brewers (I also had a fourth that I personally had back then), and I was able to serve 25 taps at our wedding.
For something quick but I want to bring a whole keg, I'll just use my direct-draw attachment that I built (it is a stainless disconnect with the chi-company fitting specifically for perlick 650ss faucets, and just use the restriction there to serve), with a CO2 tank.