There are many flavours that can be added to the bag to enhance the chicken. A dash of olive oil or knob of butter will enrich the meat. You could try adding different herbs – thyme, tarragon and rosemary would all work really well.
For a luxurious meal, try adding a dash of truffle oil or even truffle slices under the skin of the chicken.
If cooking the meat as part of an Indian meal, you could rub the chicken with spices such as cumin and coriander before cooking, just bear in mind that the flavour will be much stronger than in conventional cooking techniques so you will not need to use as much.