I've played a number of outdoor gigs over the years. Here in Southern California, bugs and mosquitos are not as great a problem as they may be elsewhere in the country, nor is the daytime high humidity an issue. However the problem Scott mentioned with the keyboard display can be significant.

I always take a market umbrella on daytime outdoor jobs to provide as much shade as possible. I tell my clients that it's not because I personally mind the sun, but it's so I can see my keyboard display. To further help with this I've made a small cardboard sun shield which I tape in place over the keyboard display to afford some additional glare protection. (My display doesn't tilt, so I will get glare if I don't shield the display and the glare can make the display unreadable.)

Another problem that I don't have a good solution for is being able to see the red LED's above my keyboard buttons. These lights let me know what settings I've selected, such as voices, etc. They simply wash out in daylight, even with use of the market umbrella. So at times I end up with unplanned voices as I switch during a number.
(I should point out that I play a SOLTON MS60. It doesn't have one touch settings or any of those convenience features. It sometimes takes three consecutive button pushes to get the voice I want and without the benefit of the LED's this sometimes gets interesting.)

I also have along a set of three or more clothes pins to hold the fake book pages from turning if there is any wind. This has helped on many occasions.

Another thing we've had to contend with in this local is dew settling on all surfaces after sundown. It's the nature of the beast out here and a further reason to have something like an umbrella overhead. But during the later afternoon hours, it's often necessary to keep moving the umbrella as the sun gets lower and the umbrella shadow moves.

At times where I've been put under a canopy, I've had to fashion a drape of sorts to keep the sun from hitting me directly in the eyes during the last hour or two before sunset.

Wearing sunglasses is not an option for me since they also make my keyboard display almost impossible to read

All in all, the outdoor gigs are a bit more of a challenge than the indoor ones and it pays to anticipate all those things that have been mentioned by the various individuals and be prepared.
Paul C.