Paper cups are good and yogurt containers also make a cute shaped mold. I made a beautiful huge candle out of one of my kid’s old slushy cups.
If you’re into grubby candles you can use muffin tins, miniature loaf pans or cake pans and then cake them after and/or decorate them with whipped wax.
For containers, baby food jars are perfect for tea lights or votives. They can be decorated with paint, decoupage and rub on transfers. Broken tiles or fake jewels with grout also make a beautiful mosaic candle holder.
Mason jars are perfect for container candles and so are sturdy old jam jars. Tea cups that you don’t use anymore but can’t bear to throw out also make pretty containers. It’s a great way to use old cups and they still look charming even if they have a chip out of them out on the patio.