Hi Caroline,
At graduate level I think an employer will be looking for is someone who is dedicated, studious, reliable, diligant, and who has a good academic record (essentially shows maturity). Some of this will come across in your CV which should be well prepared.
As an environmental scientist, field work will be at least some part of your work, especially at Junior level. This will mean undertaking baseline surveys (i.e. water sampling, sediment and soil samping) and will often take place in remote parts of the world that may seem slightly hostile. It will also involve working face to face with the potential client. Therefore, a prospective employer will want to feel that you are willing to go to remote Jungle, arctic or similar locations and that you can be trusted to convers with the client in a professional manner (again maturity plays a big roll here). Also in these situations a degree of practicality and self reliance helps... i.e. dont be afraid to put in about your time in scouts or cadets.
It is important to remember that what you actually know is not as important as your ability and willingness to learn. This is as in many cases what you have learnt in your degree will not be directly applicable to your future career and most of what you use will be learnt on the job. You probably know where to look but here are some sites:
You also need to consider your career plan. Do you want to go into further study, MSc, MPhil, PhD? If so would you prefer to start work straight away and consider studying part time or hold off on working and look.
Also I agree with what Chris put, especially use of MS office, Excel, word, powerpoint, being flexible, although perhaps PhreeqC, and groundwater models would be a bit in depth at this point. One things that you may want to look into is a basic understanding of mining. What it is? what is mined? and the different methods of mining. Also the procedures that go into modern mine developments i.e. exploration, scoping study, (pre-feasibility study), feasibility study, ESIA and permiting, construction, operation, closure, and post closure.
The structure of an ESIA with swing towards mining (you probably know how this works), public consultations, baseline studies, ESIA structure, permitting procedures etc
Finally you might want to look at familiarising yourself with the environmental and social impacts of mining such as acid rock drainage and metal leaching (ARDML), dust, loss of habitat, loss of agricultural land, etc. As an environmental scientist you are expected to be a jack of all trades and need to know a bit about everything as you are going to be writing ESIA chapters from specialist reports i.e. ARDML reports, water quality sediment, soilds, socioeconomic baselines, etc.
Hope this helps
Andy