I recently did a basket weave on a rather large cake and by the time I got to the last of the buttercream icing in my bag, it was oily and warm. Any ideas on keeping it cool as you ice?

Sometimes I have two bags of icing. While I'm using one, I lay the other on some frozen gel packs (like for lunchboxes) or in the refrigerator. When one gets warm, I switch to the other.

HTH.

I don't do well with disposable plastic decorating bags because my hands get too warm and soften the icing. I use parchment bags instead.

Have multiple bags handy; don't fill them very full; eventually you'll get faster at it so your hands aren't holding the bag for long periods of time.