I have similar 'concerns'. I intend to start on my 1st CF in mid September. None of us can predict what nature will have in store weatherwise. I'm sure all of us doing the Camino for the first time will have exactly the same concerns too. Though there is an enormous variety of equipment and gear available to us, getting that final choice of kit - that delicate balance between functionality and weight seems to be critical to success. I did finally decide to purchase a sleeping bag - the Highland Trekkie. At about 600g it is quite light as sleeping bags go and is quite cavernous in length. I'll use it in conjunction with a Rab silk liner. Whether or not it was a good decision I'm about to find out in 13 weeks time. It'll be in my pack. A factor that influenced the decision is that I'm told the same sleeping bag is stored in one of the outdoor shops in Pamplona. Should the weather be bad and the albergos be cold and the Highland Trekkie not up to it I can buy a second one early on during the Camino, though it'd cost over twice the price that it did to purchase it in the UK!!!
I'm trying to be optimistic with regard to the weather and this influences my choice of clothing. For baselayer tops I've gone for 1 long sleeve Icebreaker (Bodyfit Basics 200) merino , 1 Icebreaker Cool Lite short sleeve, and 1 Rab Merino 120+ long sleeve top. I hope to wear the Cool Lite and the Rab most of the time as both are merino blends, more suited for warmer weather and quicker drying than the long sleeve pure merino top. The more substantial Icebreaker 200 long sleeve top will be my baselayer for 'bad weather' days. I'm still not decided on what to wear to sleep in so I could be persuaded to throw in a pair of light weight tracksters! For cold/cool/windy dry weather I have the excellent Montane featherlite top that weighs all of 60g as a windbreak. As a general walking 'jacket' to take on this 5 to 6 week venture I decided on the Outdoor Research Ferrosi smock. I love it. I have also packed an old but cosy Jack Wolfskin Gecko fleece to wear at the end of each day. For walking trousers I've got Craghoppers Kiwi Plus and a pair of fairly old but very good Columbia convertibles. For wet windy days I'd wear Berghaus Paklite overtrousers. Here in the UK my go to choice of waterproof jacket would be the Paramo Adventure Light smock. It's superbly effective and has a beautiful soft feel, but at 560g and not being particularly packable I have reluctantly decided to leave it at home. Instead I've bought the
Altus poncho!The clothing choices have been based on walking in the weather conditions that we have faced in the UK so far this year. Months of wet and cold weather turned the countryside into a quagmire up until mid May. There were two particularly wintry spells where the sub-zero winds came at us directly from the depths of a bitterly cold Eurasian continent. Since then temperatures have rocketed on several occasions to 27 Celsius and the weather has been dry and sunny in the main. So I know that my kit will cope with these extremes. I have not yet tried the poncho as it is bright red - not my colour choice I'm afraid. I just hope it does the job if needed whilst on the Camino.
At the end of the day you have to make some compromises. My main priority has been to keep the weight of the pack down to as low as practicably achievable. This is so so so important over a 5 to 6 week period. Adaptability has been the key to human survival on this planet. I just hope that given the final choice of clothing that I have made I am able to find some combination of it that allows me to adapt reasonably comfortably to whatever I have to face on that day. Inevitably there'll be periods of discomfort. But although you should never take comfort from someone else's misfortunes it's often the case that no matter how much you suffered on the day someone else somewhere will have had an even worse time of it than you had.