You can adjust the spice level of your seasoning by how much cayenne pepper you add to the mix. Generally, 1 teaspoon will result in a mild jerk seasoning, 1 1/2 teaspoons a medium level, and 2 teaspoons being medium-hot. This, of course, is different for everyone.
If you don’t have allspice, combine 1/2 teaspoon cinnamon, 1/4 teaspoon nutmeg, and 1/4 teaspoon ground cloves. This would be in addition to the other spices to substitute for the allspice in the recipe.