I'm also a Focus owner who is crap at reversing. (Come to think of it, I'm not so hot at going forwards slowly either!)
I generally find it better to reverse in to a space on the basis that coming out in to the traffic stream forwards gives better visibility, and is thus safer.
WRT shopping, I always put my supermarket bags on the floor behind the front seat. If I put them in the boot, everything falls out.
Friends whose parking skills are superior to mine, including an HGV1 driver, have all commented on how difficult it is to judge the corners of the Focus, especially the rear.
Chris