The screenshot shows my situation and full inventory - I'm playing hardcore mode and have full health but only two hunger drumsticks left. My wheat farm is just five blocks (two can be seen in the picture - the other three are just out of shot and were planted at the same time). I have a self-imposed animal-friendly rule, so I can't go and kill a pig. I found no mushrooms in my locality.
I'm standing in a hole in the ground waiting for the wheat to ripen. Is it worth the wait, or am I likely to starve before that happens?
As an aside, I recommend animal-friendly, vegetarian hardcore mode as a bit of a challenge. In my case it was made doubly difficult by spawning in an ocean (is that a glitch?) with just a couple of small treeless islands nearby. Had to swim for three minecraft days and nights before finding land with trees. On the way I found another small treeless island where I collected the sugar canes and killed a zombie. (Would that it had been a skeleton - I might've been able to craft some bonemeal!)
So, if I stand still my hunger bar doesn't deplete? That's good to know.
I have zero bonemeal (my full inventory is shown in the screenshot), but all five farm blocks are next to water. None is illuminated by a torch though, so I suppose that will slow growth down (no growth at night?)
Ideally I'd like a skeleton or two to come and stand by my peephole, close enough for me to murder. But it hasn't happened yet.
I did eat one piece of zombie flesh on the way - it poisoned me. I'm not sure I got any nutrition from it.
I know you're playing hardcore mode, but what difficulty do you have the same set on? On easy you'll only starve down to 5 hearts, normal you starve down to half a heart, and on hard, yeah, dead. Corrected, and not rudely! I'm impressed.
Also, protip for eating zombie meat, eat it and stand still till the hunger debuff is gone.