If you can watch the MK Festival of Fantasy parade from Frontierland, there are some large square platforms along the storefronts that allow for seating along the edge. There's no back, but it's better than sitting on pavement, and the view is great. The platforms are slightly elevated so that, even if you're seated, your head is at the level of those standing, so you aren't blocked. That section of the park is usually much less crowded than Main Street for the parade, and you'd stand a good chance of getting a spot on the edge of one of those platforms probably 30-45 minutes before the parade, maybe less during less crowded times. As far as the MK fireworks, if you can spring for the money, the Tomorrowland Terrace Plaza View dessert party could be an option, at $59 a head. You get a table to sit at and a nice spread of desserts and drinks, as much as you want. Just before the fireworks, you're escorted to a reserved viewing spot in the Hub that isn't crowded and has a great, straight on view of the fireworks and castle projections. There's no formal seating, but many people move to the back of the area and more or less lean on the top rail of the low fence that encloses the section. At least you would only have to stand for the duration of the fireworks and not for a hour or more before to stake out a spot.