Turkmenistan has a hot, dry, desert climate. During June and July, you can expect temperatures well into the 40s (degrees Celsius) during the day, and dropping to 30 or so at night. It’s very unlikely to rain during this period. On either side of that, around April-May and September-October are quite comfortable with temperatures around the early 30s during the day (though it’s possible to experience late 30s or early 40s during these times as well), and dropping to the mid-teens overnight. It’s still unlikely to rain. Winter temperatures usually don’t get above 10°C and regularly drop to below 0°C, and it is much more likely to rain between November and February. It does snow most years, but usually only once or twice, so most of the time there won’t be snow on the ground.
So depending on when you’re visiting Turkmenistan, you might need anything from shorts, t-shirts and swimming clothes, to jackets, boots and scarves.
You may be thinking of Turkmenistan as an Islamic country and therefor be wondering about what’s appropriate for you to wear, but you don’t need to worry about this aspect. They are technically Islamic, but what they have is a complicated and unusual relationship with religion, and although they are more conservative in many ways than most western people, it’s not in a religious way. You won’t see many local women showing much skin, though plenty of the local Russians will be, and it’s certainly not unacceptable for you to do so. Likewise local men don’t often wear shorts, but it’s not because it’s inappropriate, it’s just not fashionable.
There will be a fair amount of walking throughout the tour, but mostly on flat, paved surfaces, so as long as you’re comfortable you don’t need to worry about anything specific. There are a few times when you might be walking over dusty or rocky ground, but nothing that can’t be done in your normal trainers, flip flops or sandals.
You’ll be transported between your accommodations by buses or cars, depending on group size, with plenty of space for luggage, so you can really bring whatever kind of bags you like. You won’t need to carry your own luggage very far at a time – just cars to lobby to room and back, and it doesn’t need to be compact to fit into small areas. Hard suitcases, soft suitcases, wheels, no wheels, backpack, whatever you like is fine.
Pharmacies are aplenty in Ashgabat and other cities, and some basic medications like paracetamol are extremely cheap. However outside of the major cities there isn’t any access to medical supplies, so it’s definitely a good idea to make sure you’re stocked up anything like that that you may need..