If you're truly using a bag as an investment, relegate it to special-occasion status. But if this is your one big splurge, definitely buy a bag that you're going to use all the time -- what's the point, otherwise? So, you probably shouldn't go for a tiny, bejeweled clutch -- you want to look fabulous, of course, but you also need to consider function. Think long and hard about what you want this bag to look like and what it'll be hauling on an everyday basis. Do you want it to fit tightly over your shoulder, or do you like a longer strap? Do you want lots of pockets or a more streamlined look? Slouchy or structured? All these are important things to consider when you're shelling out for a bag that could last for 20 years.