Sizable is a good way to describe something that's large or ample, like the sizable bowl of baked beans you ate before climbing into your sizable tent at the campsite.
When something's big enough — but not necessarily enormous — it's sizable. Your family's sizable minivan is big enough for you and your siblings, although you can't fit the whole softball team in there. The sizable fish tank you bought offers plenty of room for your three goldfish, but your sister's bettas will probably need their own tank. And if you skipped lunch today, you might want to order a sizable portion of spaghetti for dinner.