Tesco vouchers die on you if you don't use them within 2 years. For anybody who is not aware of your current voucher life remaining: GO NOW to your Tesco Clubcard account and click on vouchers - all will display the expiry dates.
Not got any use in mind? No problem - buy 50p (which gets you £1) in Delivery Saver Plan coupons. The remaining balance on your coupon will be given back to you in 'change' with another 2 years of life. Leaving you free to build up a bigger total towards something good. Perhaps Tesco will bring back the Boost Events in time? This way you can stash your coupons for better usage.
How does it work? Say, you've got a £50 voucher - but it's going to expire, oh no. You spend 50p on the £1 Delivery Saver Coupon. You get back £49.50 in change with a new 2 years life on the voucher.