off the cuff:
Non-novelty condoms are regulated by the FDA. If it hasn't passed its expiry date or been compromised in some way, you can literally put your entire forearm inside without it breaking.
Never, ever use oil-based lubricants with latex condoms. Put a bit of vaseline on your fingertips and rub a condom between them, then try to stretch it and you'll see what I mean. Use water-based lubes, e.g KY.
Always carry unexpired condoms and keep them in a cool, frictionless place. Back pocket: bad. Wallet: bad. Purse/murse in a pocket without hard utensils: good. Rolled down fold of your sock: good. Only use condoms from a package that has a 'pillow' of air in it.
Some people have latex allergies/sensitivities. Google suggests no studies have been done on how common this is. Polyurethane condoms (avanti or whatever) are much more expensive, but if you want to cover your bases, carry one of these with you. They don't stink like latex, they are thinner, but they're a little crinklier on the whole.