No matter how many days the trip, my packing regimen follows these rules:
1. Luggage - no more than what I can handle with 2 hands, no matter the weight. One piece is a 20 in Hartmann pullalong, with one Le Sportsac collapsible bag in case I purchase too much along the way and overflow the Hartmann. I'll beg whatever to get airline to allow me to carry on these two pieces plus a shoulder bag. If not, I check the Hartmann, which would be packed with the heavier items.
2. Clothing/shoes - if old clothing is sufficient for whatever purpose the trip is, I chuck the old clothing/shoes as I go along. Plus tight packing of old clothing doesn't matter as once worn, will be chucked anyway.
If I don't chuck the clothing, and I still have too much, I mail the unessentials home by cheapest seamail method.
3. Purchases - only buy what I can use on the trip, or is compact enough to fit into my luggage. If buying more bulky stuff, only if retailer will mail it for me, and in many US cities/states, the savings on local sales tax will partly cover shipping cost.
4. I rarely bring my laptop on a trip, as it's heavy and bulky. I would use an internet cafe for email, etc., and any special files I need, I upload them to my website before the trip. If I need to update these files along the way, I would email them to myself if I cannot ftp the files to the website.
5. Money - I carry cash, and use a credit card for hotels. Overseas, paying cash, you usually get best discount when buying something. My negotiating strategy is, when I make my final offer, I just lay the cash next the item in question, and tell the retailer to select which he wants to pick up - 9 times out of 10, they will pick up the cash, and I pick up the item, even if my offer is only 30 or 40% of the original (but not inflated) price. If the retailer refuses the cash, I pick that up and leave, but you have to be prepared to forego the purchase. If you walk out, about one third of the time, the retailer calls you back.