If you can, exchange money at a bank and not an exchange stand. you get more value that way. Also, it may behoove you to open an account at a bank that has international branches like HSBC of research some others.
They money exchangers in Gibraltar (main street, not the airport) typically give 1% to 2% better than the banks, so I would double check that where ever you go.
I keep my passport on my person at all times when I am out of the house. The Guardia Civil and local police here set up roadblocks all the time, and you must show your passport if asked for it. Also, you have to show your passport coming and going from Gibraltar/Spain so it really can't be avoided here.
Get a leather cover for your passport, you can buy a decent one for around $10 or go for something nicer (I have a Montblanc one), otherwise they quickly show wear and tear.
High quality, durable, rolling luggage is a must. With a two bag limit, I take a rolling Samsonite carry on and my matching laptop bag slides over it's handle. With a one bag limit, I check my suitcase and carry a backpack with an inner laptop sleeve. Samsonite has a patented 6 wheel rolling design that lets you turn the bag sideways from either side to get through tight spaces, highly recommended.
Keep in mind that while you may be able to depart with a two bag limit, you may transfer or return at an airport with a one bag limit (Gatwick in London for example). Some budget carriers like Easyjet are militant about the one bag rule, even going so far as to make you check shopping bags from the airport once you reach the boarding desk (they are idiots, avoid Easyjet at all cost).
Some carriers let you check in online up to 24 hours before boarding, so you can get your seat before the rush. If you aren't in business class, choose the emergency aisles more more leg room.
I keep a plastic sleeve multi pocket thing with a snap on it in the side pocket of my laptop bag with my itinerary and plane tickets and a PEN. This makes getting to the documents quick and easy and keeps everything well organized. Receipts can be put in the pouch for doing expenses later.
I always keep my wallet and passport in my front pants pocket. It's harder to pick pocket this way, doesn't fall out easily, and is more comfortable than sitting on them for long distances. I'm also much more aware of them there than in my back pocket.