A trader works on the floor of the New York Stock Exchange.NYSEThis is CNBC's Morning Squawk newsletter. Subscribe here to receive future editions in your inbox.Here are five key things investors need to know to start the trading day:1. Tiptoeing toward a winning weekStock futures are little changed after the Christmas holiday break this morning, but the three major averages are still headed for weekly gains.Here's what to know:The S&P 500 is up 1.4% this week after setting new intraday and closing records ...