I've always been told that insulin pens not in current use do not need to be kept cold, only the ones that are not currently in use (therefore might be around for quite a while) should be stored in the fridge until they're used, then they can stay out of the fridge as they're only going to be in use for days/weeks up to a couple of months so they won't denature in that time as long as they're in date.

I've always worked that way and I use my lantus pens over a couple of months and there's never been a problem. When I finish one I go get a new one from the fridge and that then doesn't go back into the fridge!

So I'd say you'll be absolutely fine! Nothing will happen to it over 4 days! If flying though don't let it go in main luggage as it gets very cold in the storage part of the plane and could freeze and denature so always put it in hand luggage!

I always take my prescription form with me when I fly just in case (I've been told ideally it should be a doctors note though) because of all the fluid restrictions, luckily it's such a small volume of fluid it's considered safe and only once have I been asked to get it out for checking, even then they didn't want a prescription just asked "are you diabetic?" I said yes and they gave it back to me! (I'm not from the US though so I don't know the restrictions there, this is just for flying in/out of the UK where we have had quite strict fluid restrictions hence me taking the prescription just in case)

I believe this response is correct as well. My husband travels 50-100% of the time with his Lantus and has never been given an issue or brought ice. He throws it in the mini fridge in the hotel when there is one (there is not always one). For longer trips we've lugged around a few pens w/o trouble. These were all within the US so outside the US I would seriously consider a Dr note

It has been years since I was on MDI and used Lantus, but I don't recall ever having a problem not keeping it cool. As far as security in US airports, I agree with previous posts about taking in carry-on. I bring it with the original box, which includes the pharmacy label that has the prescription info.

I spend a lot of time outdoors, often in the backcountry where I need to take insulin with me and don't have a fridge to carry around. It depends on temperature, though:

Cold - If I'm going to be outside and it is cold (below freezing), I keep my insulin in the same case as my meter, and put it underneath some layers in a pocket close to my body during the day. When I stop at night, it goes in my sleeping bag (same idea). It has never frozen doing that, though I know it's gotten fairly cold because my meter will not work if it is too hot or too cold.

Hot - If I'm going to be outside and it is too hot, I often keep it in the same case as my meter, and I put it inside my pack so that there is no direct sunlight on it. This I've never had to do, but could logically work: To help even more, wrap the bottle in a wet hankerchief and not in direct sunlight. Water changes temperature more slowly than air, so it is a way to naturally insulate it. Whenever you get to a cool stream, go ahead and re-wet your hankerchief. Just remember to wipe the bottle off with alcohol before using it to kill any bacteria before it transfers to your syringe and inside you. I've been out all day in heat over 100 degrees and my insulin is always fine.

If you are traveling in climate controlled environments, then no worries about insulin temperature unless you plan to travel for more than a month.

ETA: I use Apidra, so the temp. suggestions are based on my experiences in various environments with that.