You have probably figured this out by now, but yes, you would say "מיץ תפוזים" for "orange juice." :)
Orange juice is ALWAYS called מיץ תפוזים, no matter how many oranges are in there , or how many people are drinking it. This is guaranteed, as I come from a native Israeli family and have asked to make sure.
They told us in another section there's no plural female word for ducks. What the heck?
You can all see for yourself with a translator, no need to wait. Grape juice: מיץ ענבים , strawberry cake: עוגת תותים , ... pineapple cookie: עוגיות אננס . Although, Banana bread: לחם בננה ... strawberry ice cream: גלידת תות (so ice cream is plural then when it's specific types?! Why isn't strawberries then plural?) Is it arbitrary? (singular: גלידה)
It's a lot more fluid than you might think. עוגת תות sounds to me as natural as עוגת תותים, and גלידת תותים is surely rare but doesn't sound very strange. I never heard of לחם בננה; I'd tend to say עוגת בננות but wouldn't blink to hear עוגת בננה. While מיץ תפוזים and מיץ תפוחים are dominant, I'm quite sure I've heard מיץ תפוז and מיץ תפוח, and hearing them today I'd think they're only a bit odd.
The only rigidity I find in a quick glance is to use ענבים - saying ענב (or the formal עינב) in any of these combinations would strike me as very odd. On the other hand, אננס and מנגו are usually אננס and מנגו even if you're talking about several whole items of fruit, let alone in מיץ or גלידה.