WTO has 164 member countries and we are already a member. It is nothing scary at all and we already trade with many countries on WTO terms including USA. Some companies who trade with both EU and non EU traders and say it takes about 15 seconds to complete an electronic form if non EU.
Some of the countries we trade with via EU have already offered us the same terms when we leave EU. Canada is on record as stating they can offer us a better deal than they give to EU.
We can still trade with EU just do so on WTO tarriff rates. At the moment we pay a high tarriff on clothing from EU and WTO rates is lower for clothing so clothing would become cheaper.
Does it really matter if we can't get non priority goods for a couple of months eg. exotic fruits as long as we can get everything we need. Medicines will be flown in if ports clogged up.
In the long run we should be able to join the Trans-Pacific Partnership Agreement to trade with Australia, Brunei, Canada, Chile, Japan, Malaysia, Mexico, New Zealand, Peru, Singapore, and Vietnam. This is a loose trade agreement which will not prevent us trading freely with other countries. Also trad with EU through WYO.
Scaremonger do not tell you the truth.