The main difference in swinging a 7-iron and a driver is that you want to hit your driver slightly on the upswing, or at the lowest point of the swing. There are coaches who want their students to practise with a 3-iron thinking that if they can hit a 3-iron all others will be a piece of cake. Perhaps this is true, but this could be looked at as back to front -- because it's easier to learn to hit a good 7-iron first, so when moving to a 3-iron it would not be an issue.
If you rush to the course with little time left before heading to the 1st tee, use the minutes available to hit a few chip shots. The chip shot is just a short version of the full swing and hitting a few chips tells your muscles and the golfing brain to get ready to play. So, try and resist running to the range for a few frantic full swings -- which may loosen you up, but it can ruin your tempo for the day, whilst touching on some possible negative thoughts.
Some golfers would rather use the limited time by hitting a few putts but putting quickly and missing more than you normally would might make you step onto the 1st tee doubting your putting ability. To warm up in a hurry whilst arousing your sense of feel and touch nothing will be better than a few chip shots. This will put your mind on the business at hand -- which is to play golf.
Out of Bounds: "I've got the wrong shoes on" was perhaps the most pathetic excuse I've heard from a golfer playing badly.