Hi! I think you are talking about a career in customs, i.e. working for a government agency. That is an absolutely fine career choice and one with lots of options, but I'll make this advice a bit more general.
I think any job that enables you to grow and build your professional skills will be good for your future career. If you are just starting out, it's helpful to find a role that will help you build your professional skills -- things like punctuality, reliability, ability to learn, teamwork, communication -- that you start building in school but have a bit of a different feel in a workplace.
If you are looking to optimize your career prospects in the future, it can be helpful to think about where there will be demand for the skills you are building. It's hard to predict for sure, but I believe the skills that are going to be really necessary to succeed over the next few decades fall into a few categories.
First, there are soft skills - like interpersonal dynamics, customer service and creative problem solving. These are things that are so important to getting things done in big organizations and bureaucracies, and they are so valuable.
Next, hard technical skills. Being proficient at computer science (latest skill sets in high demand seem to be data science and machine learning, but it evolves quickly) is something that will continue to be valuable as the world turns digital.
Finally, many people opt into public sector work as a way of ensuring more stability. Government roles often come with longer-term employment prospects and pensions earned with long service, so if you are passionate about public service that could be a good avenue to pursue.
No matter what role you are in, it's important to think about what you are learning and how you could apply it in the future. There is learning to be had anywhere if you have the right mindset.