Luggage and bags:
Be sure there is extra space in your bags for clothing and souvenirs you'd like to buy and bring home. Clothing is cheap. For example, men's dress shirts are $3.
Clothing/Shoes/Weather Gear: Don't bring shorts. People do not wear shorts here, even in 120 F degree heat. Young male children, however, may wear shorts and tank tops. Exception - if you look like a foreigner (e.g. Korean, Chinese), you can get away with wearing shorts in the big city of Lahore. Short-sleeved shirts, even T-shirts, are OK (which was surprising to me).
Bring thin fabric, loose fitting clothing, especially if you're coming to Gujranwala in the summer, which for all practical purposes, starts in April. I went at the end of April and by the beginning of May, the temperature was typically 105-115 F.
Toiletries and Medical Supplies: Antibiotics - when you get sick from the water or food containing bacteria that you're not used to. If you're not from Pakistan, don't even brush your teeth with the tap water. Close your mouth when showering. Bottled water OK. Filtered water not.
Iodine tablets - for purifying water in case you're out of bottled water.
Toilet paper - some places will have toilet paper, but some places won't. That's why the little water spigot next to the toilet - it's for you to wash your hind end with your left hand w/out toilet paper.
Deet - Some mosquitoes, especially in the outlying village areas
Anti-malaria drugs - I'd take Malerone, especially if your trip is short. Mefloquine gave me side effects of insomnia and nightmares!
Common medications - If you're from the U.S., you won't find any Tylenol or such familiar drugs in the pharmacies in Pakistan.
Wet wipes - many places in Pakistan are unsanitary and prone to disease. Wipe your hands before eating or touching face. Alcohol wipes even better.
Photo Equipment: Be sure to bring your voltage converter. Pakistan is 220v, for use with electrical plugs with two round pins.
Camping/Beach/Outdoor Gear: Respirator - like what painters wear to filter out fumes - the air at night is especially polluted.
Flashlight - frequent blackouts, especially in the warm and hot months.
Miscellaneous: Bring CASH! - Very, very few places will take credit cards, ATM cards, or traveler's checks. U.S. dollars are OK. Remember, cash. There is a Citibank in Lahore, but that means you'd have to take a taxi ride for 1.5 hours from Gujranwala just to get cash, and only from a Citibank credit card and Citibank traveler's checks. The airport exchanges only cash too.