I have been putting together a list of things my department has achieved in 2019. It has cheered me up no end. I've asked my colleagues to review the list and add anything that I have missed. I've laid it out in a simple tabular format
- Where we were at the start of the year
- Where we are today
- What we will do in 2020
I think it is a good idea to keep a work journal. Sit down on Sunday night and write down everything you achieved or what went well in the previous week. Not only will it help with the Monday blues it will help you review your CV and as Skeleton567 mentions, give you ammunition for any performance/salary review.
If you are a manager then it helps to write down what your reports have achieved during the week as well. Sometimes the benefit of a quiet (and honest) thank you far exceeds the effort it took to say it.