Any activity will extend the 18 months so point purchases, purchases using the Barclay Choice Visa (generally offered without an annual fee and shifting signup bonuses), or purchases through the Choice Privileges online shopping mall (the purchase of a single music track through the iTunes store is usually the lowest cost option) will count as activity. Use of points for things like magazine subscriptions or conversion to airline FF programs (Southwest is the most lucrative option, but none of these transfers occur 1:1) will also extend the life of the points. As some of these activities take time to post, it's advisable to do them well ahead of time--I'd leave six weeks for safety's sake.

Although you may not want to do a stay, one of the advantages of a stay for points activity purposes is that it's the date of the stay that counts so you can push the envelope a bit compared with the other options. Although Choice's loyalty program does not provide much in the way of benefits or even recognition--I frequently get surveys after my stays from the hotel or from Choice that include questions about recognition so I know the program thinks it's important, but I generally am acknowledged no more than 1/3 of the time while the benefits might include a slightly better view of the parking lot but rarely anything of true value--as GUWonder has noted, there are strategic uses, mostly in Europe, especially in Scandinavia, but I've got one or two go-to redemptions at 8K in the US that save me a fair amount of money for a pleasant hotel in decent surroundings.