Not so sure about the explosives - personally I’d be pretty keen to have a bunch of claymores as some form of final defensive fire to create enough confusion to give you a chance to get the hell out of there.
Well, I guess it depends on your objective. If survival is key, then I’m thinking that you aren’t in it for a prolonged fight. This means breaking contact with a retreat to an area of reasonable safety. With regards to combat load and weight, a modern assault gun seems obvious to me. I would eschew the M4/M16 rifle for an Ak-47. I prefer the greater knockdown power of the 7.62X39mm round over the 5.56 of the M4/M16. The Ak round is reasonably small when compared to a full rifle round such as those found in bolt-action surplus rifles. It allows you to carry a reasonable combat load, and the removable magazines allow for quick re-loads. They also have a semi-auto function, though the M4/M16 also have 3-round burst capability that could be handy in a pinch. As a back-up, I can’t think of anything less than a .45 ACP semi-auto pistol or submachine gun. The round is just not that much heavier than a 9mm, though most modern semi-auto pistols in 9mm do carry more rounds in a magazine than a .45. I would still want the extra knock-down power. Even if you don’t get a “kill”, it would still give you the extra few seconds you might need to escape their grasp. Last but not least, some form of mace or club for last stand scenarios. No spikes, since they could become stuck in flesh and delay another swing at a crucial moment. Something more along the lines of an American Indian’s war club. Well balanced and effective without weighing too much. If you are looking at eradication of an entire group of zombies, then a Mk 19 grenade launcher would work. It would have to be in some sort of crew-serve mount on a vehicle, but the devastation would be awesome. An M2 .50cal would be almost as good. If you want to “plink” zombies at distance, then any good sniper rifle would work. For those really long shots, a .338 Lapua or .50 BMG Barrett rifle would work really well. In a really morbid way, that could actually be a lot of fun!