First of all, always have activated charcoal with you! It's great for pushing through any toxins you may have ingested. It can settle your stomach quickly if you've eaten something that disagrees with you—or if you've just had too much of a good thing.

Here are some homeopathic remedies you can take with you—and they are good to have at home too! I suggest the 30c potency—take every 2-3 hours until you notice improvement. If not better after 24 hours, try a different remedy or contact your homeopath.

Podophyllum
The first remedy to consider for acute diarrhea.

Symptoms that point to the need for this remedy are:

Sudden, explosive diarrhea
Gurgling through bowels, then profuse, putrid stools gush out painlessly
Stools light, like water; foaming; with meal like sediment; then weakness
Diarrhea better lying on abdomen; worse while being bathed or washed (children)

Arsenicum album
This remedy has the typical symptoms of food poisoning and turista with terrible pain and restlessness.

Symptoms that point to the need for this remedy are:

Diarrhea and vomiting at same time
Violent pains in abdomen, with anguish and restlessness
Has no rest anywhere, rolls about on floor or bed and feels like they’re going to die
Stools may be like rice water, foul, small, involuntary, acrid, burning, black
Feel generally worse if drinking cold drinks, with much prostration

Nux vomica
People that might need this remedy tend to overeat and over-drink—and suffer the consequences.

Symptoms that point to the need for this remedy are:

Nausea; wants to vomit but can't
Violent vomiting with spasms and cramping
Food lies like a heavy knot in stomach
Hiccup: From over eating; from cold or hot drinks
Craves piquant food; beer; fatty food; chalk; stimulants
Tends to overeat and drink and feels worse for it
Bowels cramp here and there

Again, if not better after 24 hours, try a different remedy or contact your homeopath.