Due to the political climate around the world at the moment, the stock and currency market has gone a bit volatile. This has pushed the pound up, and the US dollar down and the current exchange rate has hit £1 - $1.30. Even though that is nowhere near the highs of 2015-2016 high's of about $1.50, but it's at least starting to strengthen a little.
Is now the time to buy your spending money?
I'm not one to speculate on financial markets, and I have no idea what direction the value of the pound will go in. If you are buying spending money to take in cash (rather than just paying with a 0% commission card over there) you need to be thinking about getting the most dollar from your pound. As we don't know how Brexit will be handled or what is going on with President Trump, the currency could swing either way depending how either of those scenarios pan out.
A good rule of thumb is take advantage of any spikes in currency value, and get at least some spending money. Don't lose sleep over the rates, buy at a rate you're happy with, don't try to bet the markets, and budget for the dollars you have bought.
Keep in mind retail currency rates are usually a few points below the actual wholesale rate. So with the rate being $1.30, you'll be looking at around $1.27-$1.28 in shops.