@bentog I did it all in Unity, so making the physics was just the case of creatively using what they provide with the engine. Same goes for the water and skybox, those come bundled with Unity as example assets. All I had to do was to come up with the idea for the game, code it and make all the geometry for the island/objects, few textures for the effects and to make this stuff to work and swap when needed. I recorded sound on my headset and edited it in Adobe Audition (which to be honest I've launched for the first time in my life). I used basic materials without any textures or UV mapping on objects to save time. Objects are reused and just slightly remodelled or rescaled/rotated to get the variety.
That's my first Ludum Dare or any game jam entry to be honest and I've spent all three days on it with regular sleep and breaks for walking the dog and eating so it was pretty busy time :)
I've been working in the "AAA" biz for good few years so I guess the speed comes with the experience in it and those "you need to make milion times for tomorrow" moments. Now I'm trying to do something on my own and have fun :)