The reader is left to try to make sense of the meaning. eg Perhaps some survivors have foodstuffs and medical supplies, and are being urged to share with other survivors who do not.
How about "I send this message to any survivors, having enough foodstuffs and medical supplies?" In that case, who has enough foodstuffs and medical supplies?
I suppose there could be groups of survivors - perhaps I am one too - and they are visiting districts to give assistance to others if it is needed
- I am letting them know that I'm OK, so they should use their efforts in other areas - I need foodstuffs and medicine, so am contacting them in the hope they can help me
How about "I send this message to any survivors, having enough foodstuffs and medical supplies?" In that case, who has enough foodstuffs and medical supplies? The comma makes this a bit ambiguous.
Compare the clarity of this. Having enough foodstuffs and medical supplies, I
I agree with Clive that you can make the sentence unambiguous by moving the participle to the front but it sounds unnatural. It's not what you'd say in an emergency with survivor groups roaming the countryside!
I'll sign off on this one by saying: my feeling is that the participle construction is sometimes just too subtle to use. Here's an example I was thinking of ...