Jetlag, Nausea, and Diarrhea are Largely Optional
Epistemic status: my best guess at the truth, with many of the standard medical-advice disclaimers omitted
Many people I know are aware of drugs for basic ailments, but don’t bother using them because they’re too much trouble to carry around. But using a pill organizer basically eliminates this overhead. For me, having a pill organizer has dramatically reduced the negative effects of insomnia, jetlag, nausea, diarrhea, headaches, etc., and significantly increased my operational capacity. In total, it has probably increased my productivity by over 3% over the last few months, and also increased my quality of life substantially. (But note that I think most people won’t get such a large benefit). Just using the alertness adjustment drugs to curb jetlag saves me about 3 hours of productive time each way on critical trips.
Here are the exact steps I followed, which take less than an hour and cost about $30:
Get a 10-slot pill organizer (4 for $10 on Amazon). Not the same as a weekly pill organizer.
Get a few basic pills from your local drugstore, supermarket, Amazon, whatever. I suggest the following:
ibuprofen 200mg (Motrin, Advil) for pain, fever, etc. 
caffeine 100mg, optionally with l-theanine
loperamide/simethicone 2mg (anti-diarrhea)
dimenhydrinate (Dramamine, anti-nausea) 
melatonin 0.3mg (mild sleep aid)
doxylamine 25mg (Unisom, sleep aid to be used sparingly) 
This gives you 4 slots left for whatever other drugs you benefit from or are prescribed, maybe things like
aspirin 81mg (in case of heart attack, also another option for pain)
modafinil 200mg or armodafinil 150mg (suppresses sleep drive). Note that this dosage is way too much if you don’t have narcolepsy.
stimulants e.g. amphetamines, nicotine
anti-anxiety meds 
allergy meds (if these are antihistamines they could double as other things)
electrolyte pills: sodium, potassium, magnesium
Put the pills in the medication organizer, and label each compartment with the medication and dosage, using a permanent marker. You can erase the labels with alcohol wipes if needed.
Carry it around in your backpack or purse.
If those particular drugs don’t work for you, try others that do the same thing. Our civilization has invented these multiple times and there’s a good chance at least one works for your particular body.
In December, I lost my pill organizer. In the few days it took me to order a new one, the following things happened:
I had to stay up late to finish work, which threw my sleep schedule off. Without melatonin my sleep was out of phase for a few days, losing me about 10 hours of work.
I had mild food poisoning and had diarrhea for much longer than necessary, which was very unpleasant and lost me ~3 hours of work.
Someone asked if I had ibuprofen. They probably had a headache or period cramps or something for hours, or had to walk to a store. Either way, they suffered for at least an hour.
All six of the basic substances listed are over the counter, have fairly low abuse potential, and have few harmful interactions (other than, say, caffeine increases wakefulness and doxylamine decreases wakefulness). However, I highly recommend doing basic research into the substances you’re using (e.g. reading the wikipedia page), especially if you’re customizing.
: One could also add acetaminophen (Tylenol); ibuprofen has an anti-inflammatory effect which acetaminophen does not have but taking it too often can cause GI bleeding or kidney damage.
: A doctor I know suggests replacing this with ondansetron (Zofran, anti-nausea/vomiting) which requires a prescription but has almost no side effects, and is probably safe during pregnancy too.
: Hypnotics (sleep drugs like Unisom) are not recommended as an intervention to improve sleep in the long term compared to other interventions like melatonin, CBT-I or light therapy.
: A doctor I know suggests alprazolam (xanax) or clonazepam (klonopin), which both require prescriptions and are addictive. Use only in highly stressful situations as needed.