For retrieving you stuff, you can either gear up and fight to clear the area, which might not work out because you failed to do it the first time. But maybe you knocked down their health a bit before you died, and maybe you killed a few of them.

Or you can do a naked grab and dash. With nothing in your inventory, it takes only a single click to get your stuff back. If it's not a wolf or a deathsquito you can probably outrun it. Archers are harder, so stay behind tree cover as much as you can.

If something is standing right next to the tombstone, watch and wait for awhile in sneak mode. Chances are good that it will start walking around. (If it's a skeleton, it might start attacking something else which is even better.)

To help prevent tombstone camping in the future, don't run right up to the mobs, always make them run to you instead. They like to stay close to their spawn area, so if you don't pull them too far away from it, they will usually go back there. They do not intentionally camp tombstones. You just happened to die in their front yard.