Option to crop image to square? Round corners on image? Preview images?

As @peteritism noted, there are no instructions. Users should be able to see that they can use arrow keys or WASD, and when the time comes swipe gestures.

Reset button on the menu to the default values.

Simple sound effects for food eating and game over. Would be a good way of playing with HTML5 audio.

I should be able to use hammer.js for touch events, that's the easy part.

I'll also need to make the canvas load somewhat responsively, which I should probably do anyway.

Auto-play mode before the player starts, like in an arcade.

The sharable URL is monstrous due to having 2 others inside of it. Would be nice if you didn't have to use an external shortener on your own.

Obviously this only applies to new games with unchanged parameters.

The starting menu needs some TLC. Or at least some labels.

Speed/Size would be better as sliders, or radio buttons for specific choices.

I probably should have done this from the beginning but I'm putting it on the TODO list.

Some way of keeping track of personal high scores, could be integrated into the social features too.

Have the game automatically take up the entire viewport.

It might be fun to implement social sharing stuff since I haven't really done that before.