Are you going to carry both a rifle and shotgun with you? Go back and get your rifle? My ourdoor load would be first round a #4 birdshot 2oz turkey round. Also we have rattlesnakes around here, and that would work fine for that, as well as effective for self defense within 25 yds. Then alternate between slugs and #4 buckshot. If overpenatatration is an issue (neighbors close by), stick with birdshot or #4 buck. BTW, have you tested your rounds at 100 yds? I don't think any shotgun pattern is going to be effective beyond about 50 yards, even with a full choke, and buck is usually fired from an unchoked barrel.
I do not intend to be carrying a shotgun unless I am hunting. If I am otherwise carrying a long gun, it will be a rifle. It is certainly a good idea to pattern your individual shotgun with the ammunition that you have. At 100 yards, a 00 buck pellet has about the same energy as a .22 high velocity bullet at that range. From what I have read and heard from people who actually tested it, the Federal LE Flight Control 00 buck loads can consistently put multiple hits on a silhouette target at 100 yards. They seem to do best from a cylinder bore gun.
I am not saying that there are no applications for slugs. There certainly are. It is even more important to test fire your gun with slugs than it is with buckshot.
It is my belief that for those who are one of the many who do not shoot much, have a shotgun, and have the courage and resolve to help defend their neighborhood if the need ever arises, then buckshot is best.
Would I prefer that they be "well regulated" in the sense of a "well regulated militia"? Certainly. It is just a fact that most people are not, and will not put the time and effort and training it takes on the small chance that they see of needing those skills.