are planets the only thing he can feed off of or can he feed off a star or anything else?

He has also fed off the Old Power.

" He has also fed off the Old Power. "

"I saw him at a local cafe eating a sammich. "

" I saw him at a local cafe eating a sammich. "

So, it seems he can feed from a star 
 

I had forgotten about Hyperstorm...

If he can feed off a star why doesn't he?

" @TheCrowbar: They don't taste as good!  Actually, it kind of ruins everything. Why wouldn't everyone ask the same question you just asked?   He always fed off of biospheric energy before - which can only be obtained from select planets. Perhaps he cannot convert and store solar energy as well or as easily as he can with energy from planets? "

maybe he doesnt feed of off of suns because there usually in populated solar systems and he wants to minimize the deaths he causes

I've wondered this myself. It wouldn't be hard at all for him find stars with no inhabited planets. Stars have significantly more energy than planets do. It makes no sense to me why he needs planets at all. If a planet can keep him alive for an extended period, then he could camp a star for millenia, maybe more, before needing to find another.

Decades of bad writing. Galactus at this point has shown capable of eating just about anything and actually being sustained by non-planetary meals. The reason he bothers to suffer on a menial planetary diet when despite being surrounded by food - is the same reason he keeps building his planet eating converter - plot.

We could play around with a million different reasons as to why he's such a picky eater based off decades of reasoning given by writers - but he's got more than enough instances of chowing down on completely normal planets, stars or energy sources for no grander purpose than eating.

@majinblackheart: Because he doesn't absorb matter, he absorbs planetary life forces and energies. When he's eating stars, he's probably not only receiving subpar energies (hence the need to drain a billions years worth of it), and leeching off of their life spans, but he's also reducing the amount of energy they have to release when they go nova, permanently reducing the amount of planets and star systems in the universe. The suns are energy stopgaps, but planets have the true life energy he needs to stockpile and save to birth the next universe. Eating a star will eventually reduce the number of viable planets and accessibility of that life energy he needs to do his final job, it's a long term game we can;t really fathom