The weather can change quickly!
I would suggest a backpack as they are handy when traveling away from Largs for a night or for shopping! By all means, take a water proof jacket if you go before the end of September! After that, you should take a heavier coat. Trust me; they are correct when the locals say the weather can change quickly! Sturdy shoes for walking, hiking boots if you hike in the mountain areas. You can pretty much get the same items from their Woolworths' or pharmacies as you can in the USA. A camera of course is a must; camcorder can be nice.
Larg is a small seaside town in North Ayrshire. Visitors used to flock here from all over Scotland during the summer if the sun was shining. Many people still do this but not as many as did 10 years ago. It is a lovely town with beautiful views across the water to Millport.
Also when Scottish people think of Largs they often think of wonderful Ice cream as the world famous Nardini family had a large restaurant here and this was where they first started selling their ice cream from. Although the large restaurant is now closed (following some kind of family dispute) although there is still the smaller cafe still opened at the Millport ferry dock