Not sure I have time to run through all aspects regarding school trips however consider the following...

Make sure you have the Head's and parents permission (documented) and the new recently revised version of AIS23 and follow the advice in the teachers supplement. Ensure regular headcounts are undertaken and that the coach company or minibus drivers have been suitably vetted. If you are working in groups establish a system for providing cover if a staff member has to go off to find a missing child and establish meeting places. CRB checks may be required if not already undertaken (including volunteers if they are to be left alone or work closely with the children at any time). Hygiene is amongst the bigger issues to have to deal with and although wipes and hand gels have a place, supervised cleaning with soap and water is essential. If any of your children are wheelchair users you need to consider cleaning the wheels during the day and certainly at the end of the day. AIS23 is probably the best guidance to use however also have a look at the recent DoE advice about school trips. There is a recent link to it elsewhere on these discussion pages. Sorry I can't go in to more detail however I hope this gives some help.