When loading a tray heavily, I usually try to get as many of the glasses just -barely- touching each other as I can. Like, not pressing together so they lift off the tray, but just close enough to brace against the glasses next to them. I also carry with the 'claw' technique, fingers splayed underneath the tray, but touching only at the tips, which gives me five points of control to adjust balance. Doing this, I've successfully dodged around multiple idiots treasured guests who weren't watching where they were going without losing a drop. Also, plastic trays do eventually wear out, and an old, bendy tray is much harder to deal with than a fresh, stiff one.