Eurostar trains and electricity supplies in Northern Ireland face possible disruption if the UK exits the EU without a deal, the government says.
The latest batch of contingency papers for a no-deal Brexit warn rail services could be suspended without specific agreements with France and Belgium.
The Single Electricity Market on the island of Ireland may cease to operate, hitting consumers on both sides.
Brexit Secretary Dominic Raab said the UK was prepared for all eventualities.
Ministers have insisted they are striving for a negotiated agreement ahead of the UK's exit on 29 March 2019.
But they are continuing to provide information to the public and businesses about the consequences if this does not happen.
The latest tranche of documents, the fourth to be published so far, state that in the event of a no-deal exit, some train operators will have to apply for new licences, certificates and authorisations from an EU rail regulator to continue services.
Operators such as Eurostar, which currently only hold a UK licence, would be affected unless individual agreements are struck with countries on the continent.
The operator runs about 40 direct services a day, via the Channel Tunnel, from London to Paris, Brussels, Amsterdam, Rotterdam and other destinations.
Mr Raab said people should not hold off buying rail tickets as the UK would work with its French, Belgian and Dutch counterparts to ensure they were able to travel and goods could be moved.
But Labour said this would "not reassure anyone" as "ministers have barely scratched the surface of what would need to be done in the event of the UK crashing out of the EU without a deal".
In a separate development, the M26 in Kent is being shut overnight while work is done to see if it can be used as a "parking lot" for lorries, in the event of a no-deal Brexit, prompting complaints from road hauliers.
The Lib Dems said a no-deal would be a "catastrophe" but people should not be "scared" into settling for what it said was Theresa May's flawed proposed agreement with the EU.
Talks on the terms of the UK's exit are nearing a crunch point, with both sides pushing for an agreement by the middle of November at the latest.
Documents released on Friday warn of the potential fallout to the electricity market in Northern Ireland if the current Single Electricity Market arrangements that apply on a north-south basis cannot be continued.
The Department for Exiting the EU said it was keen to work with Dublin and Brussels to reach an agreement on maintaining existing arrangements whatever the outcome of the negotiations, including no deal.
But it warned that there was a risk Northern Ireland would become separated from the Republic of Ireland, in energy terms, and that this would make the market "less efficient".
In such a situation, it said regulators may have to use "fall-back arrangements" to ensure power is transmitted between Britain and Northern Ireland and to maintain the necessary generating capacity.
Mr Raab said the Single Electricity Market was the product of bilateral co-operation between London and Dublin and he hoped this would continue. Even if it did not, he said the UK would be prepared.
"We have got interconnectors and the regulatory measures that the government can take to make sure that Northern Ireland maintains the energy supply it needs."
On consumer rights, British subscribers to Netflix, Spotify and other online entertainment could see their access to content limited when they travel to the EU's 27 remaining member states, depending on what local rights deals and portability agreements are struck.
There would be no change for package holidaymakers unless their booking is with an EU-based firm and completed outside the UK - when they might not be protected from the firm going bust.
In the event of a no-deal exit, the transportation of horses to the continent could also be disrupted.
Unless the EU agrees to grant the UK "third country status" on the day it leaves, no horses will be allowed to travel to the continent - a potentially huge blow to the racing industry.
The government said it was confident the UK meets the animal health requirements to secure an immediate listing as a third country, making it subject to the same rules as countries like Australia and New Zealand.
But, it added "in the event the UK is not a listed country equine movement to the EU could not take place".
The documents also state that the UK wants to maintain the benefits of the 40 free trade agreements with more than 70 countries that it is party to from being an EU member.
Other subjects covered in Friday's documents include:
- Trading and moving endangered species protected by CITES
- Breeding animals
- Commercial fishing
- Exporting objects of cultural interest
- Funding for British Overseas Territories
- Sanctions policy
- Trade in rough diamonds
- Accounting and auditing practices
Previous no-deal papers have warned of the risks of UK flights to the continent being grounded and Britons visiting the EU facing extra credit card charges.