When you visit Strathcailleach Bothy, bring your own fuel (firewood, coal). There might be some peat at the Bothy, but when we spend a night there, it was completely wet and therefore useless. We were happy that we walked in with plenty of firewood.
The miles from Sandwood Bay to Strathcailleach are pretty boggy. The outlet from Sandwood Loch can be challenging to cross during or after rain. I recommend trekking poles to help you navigate over the slippery rocks and the strong current.