Hah! Happens to most of us.
When I was 5 years old, I visited Pakistan for the first time in my life.
I used to play in the dirt with friends and cousins, eat everything that was handed to me etc.
We used to have cows at that time and the care taker for them, Shera, a kinda mentally disturbed guy, who showers like once a year or something, I used to eat with him and lick the bowl after he had tea.
My grandmother used to yell at my mother ' Sometimes I think that he ( Me ) doesn't have a mother at all! ' I used to be covered from Top to Bottom in Mud, sand, dirt and what not- Even today, I think that made my immune system more stronger and resistant.
Fast forward 7 years- When I was 12 years old, I came back. Had diarrhea for 2-3 days, then I adjusted to normal underground water and I was still cautious about eating from outside etc.
Now- I am 18 and been living here for 19 months- I eat anything and drink anything. I do have some certain rules though- If I know that it is dirty, I refrain. I am choosy- I want my own cutlery, plate and glass. Never share with anyone else.
So, my tip is- Be careful. Wash the plate, cutlery and glass before eating. If you think other's around you ( Desi's or relatives ) will mind, just tell them that your Doctor warned you about Malaria and Hepatitis, so they do not feel offended.
You can always ask Rehri wala to pack it for you, rather than eating in their own plates and using their spoons- They get washed in 2 seconds literally and the same water is used all day.
The best and hygienic places will cost a bomb as well- So, I usually just have something to eat from Subway, Hardees etc.
I hardly eat from Rehri walas- I always keep my freezer stocked with milk, fruits, yogurt and frozen food.
Stick to bottled water and keep Juwain ( Some next kind of seeds, good for an upset stomach ), Hand Sanitizer bottle, a small jar of Karmina tablets ( Homeopathic for easier digesting, suck on the tablets or chew them ) and enjoy Pakistan! 
