Weekend traveling is a situation where less is better. There’s no sense in lugging around a huge suitcase when you’re only going to be somewhere for 2-4 days. You should try to pack everything into a small/middle-sized duffel bag which is easier to carry around than wheeling one of those annoying suitcases, especially on uneven streets and sidewalks. If you can get away with everything going into a carry-on for airline travel, all the better. You won’t have to worry about luggage getting lost in that case. Also, if you’re traveling by train or bus it’s a much better idea to have only a small amount of luggage that you have to carry and keep track of. So pack only what you are absolutely sure you are going to need: i.e. don’t bring your tennis racket or formal wear unless you’re absolutely sure you’re going to use it.
When packing clothes, remember that your main pieces (jackets, pants, skirts) should be in only one or two neutral colors so that you can pair them with your shirts/blouses that should be more brightly-colored so that you don’t appear too drab. Keep in mind that cotton and other natural fabrics are cooler but blends tend to dry faster and wrinkle less; also, light colored clothing will show dirt and stains more easily but is preferable in very warm climates. Also, if you are going to an area with VERY hot weather, remember that long-sleeve shirts and long pants/skirts in light colors will keep you cooler than shorter clothes. Depending on the reason for traveling, you’ll want to have more casual or more professional attire, but a dark pair of jeans works well for casual outings and can be dressed up easily in case of a surprise evening out.
If you’re traveling to another country, I would suggest packing either a small phrase guide or printing out some sheets with basic phrases. Knowing even a small amount of the local language will help you out a great deal (e.g. understanding signs/directions, finding your hotel or ordering a meal) and people are generally more friendly if they know you are at least attempting to speak something besides English.
It’s a good idea to think about where you’re going and what you’re planning to do when you get there. This will help you to pack and make arrangements for traveling and accomodations. However, you should also keep in mind that things will not always work out as you planned, so don’t buy tickets for every single thing you think you’re going to do or at least make sure they’re not scheduled for a specific time or make only one or two such arrangements. Trying to fit too many things into your schedule is not a good idea; instead, you’ll most likely end up stressed out and not having enjoyed your weekend.