...That said, I have a couple of players I wish weren't so ridiculous about having any given weapon instantly ready in any situation...
I take the simple road when this happens: I have the character make a LUCK check to see if they can get the desired item (it's not always a weapon) out without getting tangled up or dropping something. If they fail, the number they fail by is the number of Actions it takes to complete the swap. I count movement as an Action in this case, so characters get 2 or 3 Actions per round, depending on their level. So if they have a LUCK score of 12 and they fail their check with a result of 15, it takes them 3 Actions to get the desired item out. They can keep moving if they like, but it will take them longer than if they stop to do it.
If they attempt it multiple times in an encounter, they make each subsequent check with a cumulative +2 modify to their roll.
I would also point out that you normally wouldn't travel with a bow strung, unless you are very likely to run into danger, because it's very easy to snag your bow on something when it's strung, and it also degrades the tension in the bow over the long term. Even walking around a city it would get caught on things all the time. So normally, bows are unstrung at night during an adventure except in rare cases. I figure it takes a round to string a bow (I assume a certain level of expertise on the part of the owner).