When I'm out and about, I often pop the FT-817 and a couple of antennas in a bag. For 50MHz, I use the ATX-Walkabout antenna, although I noticed today that the SWR is a bit high on the band and I'm not sure why. It's usable though, particularly if there is Es around.
The other antenna I use quite a bit is the MP-1 antenna. I use it with the FT-817, mostly on CW from 7MHz up to 28MHz. I mentioned on Twitter this morning that I used it and immediately got a couple of 'what do you think of the MP-1' comments, seemingly with the subtext of 'I have one but I don't get on with it'.
I'm sure a dipole would work better but the MP-1 is very convenient and goes together quickly and seems to me to perform well. It's essentially a 'screwdriver' style antenna. I've had my MP-1 for around 10 years now and perhaps the connection onto the coil is not so great now. I sometimes have to fiddle with it a bit to get a good connection, but it's easily sorted. On 7 MHz with the ribbon radials, it's quite tricky to tune up, but once you get it into the zone, it's fine. I worked MM0CPS/P on Tiree this morning running 3W CW to the MP-1. On the higher bands, tuning is easy.
I don't have the tripod kit, so I usually clamp the antenna to a bench or table. There's usually something around. I keep meaning to try a photographic tripod, but haven't checked the fittings yet to see if they are compatible.
The FT-817 is quite heavy on batteries, so if I plan to operate for more than a half our or so, I use my Pentaflex power station (high capacity 12v supply). This is very useful which I actually got to power my telescope, but use it more often for radio and other purposes. I did notice that the PSU made a bit of interference on 28MHz, but moving the PSU away from the antenna solved that.
As I've reflected before, contacts with this sort of equipment feels more of an achievement than with bigger equipment and is, therefore, more satisfying I think.
Happy portable operating!