Is there some little design quirk you build into every vehicle?

[Dispatcher]

I like to equip my crewed parts with parachutes, which I set to open on impact.  

[RandomUser]

7 hours ago, MiniMatt said:

Before you know it, you're looking at a 379 ton, 169 part monster. To go to Ike.

What...  the...  f***... 

And I thought my 205 ton Orbital surveyor was too much.  Then again, my Dres craft is 1,000 tons... 

[TMS]

All my launchers adhere to a slender, tapered format.  It helps with balancing in the lower atmosphere and looks kinda cool.

Procedural Parts are a necessity, of course.

[suicidejunkie]

This is only visible pre-launch, but most of my designs employ a "bag of hammers" as a first stage.  Three for small stuff, nine to thirteen for the medium scale mun rockets.

Costs just one separator, and then pennies for the SRBs in a grid.

The main rocket stack will have a TWR of just 1.0, but the Bag-O-Hammers (tm) boosts the rocket to mach 1 in the first few seconds, and then I just run sustainer engines for the ride through the atmosphere.

[Cairol]

I put a red and green nav light on every craft. Mostly on the lander stage.
And I pretty much always add a HECS core or similar, even for kerballed crafts - just in case.
And for kerballed crafts, I tend to add at least one KAS winch to secure kerbals on EVA to the ship plus KAS/KIS containers with spare parts.
I feel better when i know that my little green dudes won't float away and are able to repair solar panels and stuff, if necessary.
When using FAR mod, I always build my SRBs with an octagonal strut on top, then a nose cone on top of the octagonal strut. Then a sepratron within the octo strut to prevent drag by the sepratron.
And yes, I know that the added weight for the octo strut is probably nullifying the advantage from the occluded sepratron. I do it anyway, because it "feels right". XD

[Sereneti]

A probe-core, in every ship.
Every ship has to have the posibility to fly unmaned.
like for testing, (i dont want my kerbals die), bring back strandet Kerbals (i try to avoid that, but...)
 

enough battery to store enough eletricity and a RTG (i think the RTG is overpowered...)