From the Operator's Manual of UH-1D/H, which are single engine helicopters:
9-13 Engine Failure - Low Altitude/Low Airspeed, and 9-15 Engine Failure - Cruise both describe the procedures for establishing autorotation. Both refer to jettisoning external loads, for instance 9-15:
When engine failure occurs during cruise flight, proceed as follows:
- Collective pitch - Adjust as necessary. Establish auto rotational glide.
- External stores - Jettison as appropriate
For civil helicopters in the USA, external load operations are covered by 14 CFR part 133, which defines several classes of external loads and the operating rules for certification. In order to be certified the helicopter operator must provide a Rotorcraft-Load Combination Flight Manual (RLCFM).
An example of an RLCFM is found here, it does not contain any special procedures for autorotation upon engine failure. References to Long Line Operations in an R44 for agricultural activities are found here.
Autorotation upon engine failure and carrying an external load are high workload situations with a higher than normal inherent danger. Combining the two is not a good idea: FAA AC 133-1B specifies that the emergency release mechanism of the external load must be demonstrated before certification.