I heard if you stay onsite your tickets and room key are on the same card. But what if you arrive before checkin time and you can't checkin ? Will they still give you your tickets?
Yes, you can go to check-in, if you're room is not ready they will give you the tickets on the room key. When you return from the parks, stop by the front desk and get your room assignment.
Who knows, you could luck out and they might have a room ready early, too
extraredstuff has it just right. We've always booked a room in Orlando off-site on our travel day before we check-in for just this reasoning. We have checked in by 8:00 in the morning and picked up tickets/keys when we've been on a package. At POFQ we had our room and were still inthe park by opening. At the Poly, we didn't get a room until almost four, but we didn't care because we were in MK!
When you get to the resort, no matter how early, you are basically checking in. You get your room/ticket cards at that time. If your room isn't ready, they will put your luggage in a storage room. They will also give you the resort number to call later. You can call from wherever you are & they will give you your room number & your key will be activated. Then, when you get back to the resort you can just go directly to your room & call for your luggage to be sent to the room. It just avoids you having to go back to the lobby/check-in area if your room is ready.
I've learned a lot from some of your questions & the responses you've gotten!
Don't worry - you'll have a great trip no matter what. I've been to WDW many many times and I still get anxious & nervous before we go, thinking I won't know about something or will forget something. And it ALWAYS works out just fine!
Make sure to write a trip report when you get back. I love reading those! They help me get my Disney fix when I have a while to wait before my trip.