Hi UGreg.
Below are my opinions, but I am sure there are some scientific errors and different opinions.
1. I did a 20 mile run this morning on normal diet day before and just bowel of museli and a coffee this morning. No water and no carbs / gels on the run. Running without water isn't a good thing generally, but I used to occassionally when cycling to train me mentally if I missed a few bottle hand ups in a race.
The running without carbs thing is being done by a few sub 3 guys in training, as you describe (no breakfast). Again in cycling I would do this to improve fat burning after the normal 2 hours exercise limit. I wouldn't try to 'bonk' or blow up but just get the the light headed feeling a bit empty type of state. I was starting to feel that today as well and as soon as I got home I cramed down a gel, 1 ltr of energy drink and then a recovery shake. Refueling straight after is key to recovery.
Also, don't try to combine energy depletion with speed or M paced intervals at the end of the long run. Your form can go a bit when carb depleated and injuries more likely if you push it.
I have also heard that having a coffee in the morning rather than carbs before this session helps to kick start the metabalism and therefore increases fat burning earlier on.
McMillian Running has some more info on carb depletion.2. l-caritine I know nothing about
3. Creatine I used a bit when cycle racing. Meant to improve sprint ability at during long races. Good to aid recovery from those bursts you need in bike races. No help to running really. Also can lead to you gaining weight by retaining more water over time.
They promote this on the IM talk website and sounds interesting, but I havent tried it myself.