I guess you are crossing via the QEII bridge?
On the north side of the river, you could rendezvous at Thurrock services. Fuel and food available.
After crossing, I assume you'll be taking the M20? The most convenient stopping points (just off the motorway) are Maidstone services and the large Shell station / waiting point at Junction 11, five minutes up the motorway - when coming from Essex - before arriving at the Chunnel junction.
If you want to find a full on greasy spoon cafe for your tip-top breakfast or some other restaurant, other than those you'll find at Thurrock, Maidstone or at Junction 11 and find fuel you'll have to be more inventive. You could for instance deviate away to Bluewater or trundle into say Maidstone or Ashford, finding the suggestions listed above. Will they all be open? Some or all of these will depend on what time it is that you intend to rendezvous with your chums and indeed how far away from the M20 you are prepared to travel in search of four rashers, two eggs, double sausage, black pudding, mushrooms, tomato, baked beans, fried slice, toast and the obligatory mug of brew.
A Google of 'transport cafe M20' turns up some ideas. Form a working group as a part part of your committee of committed Adventure (with a capital A) travellers and have them create a suitable list of locations, timings, availability of fuel and the like. I'd recommend a spreadsheet.
