Welcome to planDisney, Melissa!
How fun that you have a California Grill reservation! It's honestly one of the best spots to enjoy a special night at Walt Disney World. The views of 
Happily Ever After from up there are breathtaking, and starting the evening with a drink or two just makes it feel even more magical. Planning a little extra time before your table is a smart move!
You can stop by the 
California Grill Lounge before your reservation to enjoy a cocktail or two, but keep in mind that early access is entirely dependent on space. Guests are welcome to order drinks at the bar whilst waiting, and you're able to step out onto the observation deck to catch the fireworks. However, availability at the bar is not guaranteed (especially around the time of a nighttime spectacular). I've had the sad experience of wanting to visit the lounge to watch the fireworks, but being told there's no more room in the restaurant. 
If you're at 
Disney's Contemporary Resort and can't get into the California Grill Lounge early, another decent spot to watch the fireworks is the fourth-floor walkway near the monorail platform. It's open to all resort Guests and offers an elevated view of Magic Kingdom Park. It's nowhere near as good as the observation deck in California Grill, but it's better than missing out altogether. 
I hope that's helpful, Melissa. 
Mike