I once tried to buy medicinal charcoal biscuits and could only fimd those sold for dogs. These should be okay as my son informs me all dog food in this country has to be safe for humans too.
Long ago when I was a nurse charcoal biscuits were regularly used for wind in the gut and could be ordered from the hospital pharmacy. It must be possible to obtain ingestible charcoal as I think they still use it for some sorts of poisoning.
One other thing we did to relieve flatus was pass a 'flatus' tube up the anus an inch or two, can't remember exactly but I think it only went up as far as the start of the rectum. The outer end was placed in a bowl of water so the release of flatus was could be viewed as bubbles.
What is a reasonable minimum spend for an online grocery delivery??