As a general rule, a weak pound is good for the FTSE 100 as a large proportion of the companies that make it up do most of their trading in overseas currencies. If the pound falls and a company generates most of its profits in the dollar, for example, then those profits immediately rise when measured in sterling.The pound has fallen to a 35-year low against the dollar. Against the euro it is just eight pence away from parity. Covid-19 has not brought good news for the pound.5G is here – and shares of this ‘sleeping giant’ could be a great way for you to potentially profit!According to one leading industry firm, the 5G boom could create a global industry worth US$12.3 TRILLION out of thin air…And if you click here we’ll show you something that could be key to unlocking 5G’s full potential…Buy some companies big in the US Under normal circumstances, the appropriate response for investors in times when the pound is weak is obvious – buy shares in companies that do most of their trading in overseas currencies.These are not, to state the rather obvious, normal circumstances.Most companies are struggling. The exceptions are those that either provide essentials, or sell products that might benefit from more people staying at home. (By the way, I don’t agree with the idea of investing into companies that supply toilet paper or other products for which there is currently a shortage. Once this crisis ends, all those hoarders of toilet paper will find they have enough to last for months, and sales will reverse.)I don’t think now would be an especially good time to invest in a company solely because of Covid-19-related demand, since that may reverse as well.Also, once the crisis ends, the pound might recover. So this is a time to be very choosy.Focus on good companies that you might have considered investing in normally, but for whom you think falls in the pound provide an additional opportunity. From this list of good companies, if you can then find a company that either sells essentials or products that might be especially popular in these times and which are also big exporters, then you might have found a good investment.Five companies to look at The UK’s biggest exporters to the US are GlaxoSmithKline, Johnson Matthey, Mondi Group, Rio Tinto, and Smith & Nephew.The case for GlaxoSmithKline shares has been made many times. I would say that right now, thanks to the weak pound and the fact that the share had fallen around 23% this year, the GlaxoSmithKline share price seems quite attractive.Johnson Matthey is a leader in sustainable technologies. That might not be a priority right now, but I think this is a good company. Its shares have fallen massively over the last year, and it should benefit from the cheap pound.Mondi is in the paper and packaging business. Mondi shares may benefit from a rise in online shopping during the crisis.I am not so sure about Rio Tinto. Its supply chain has been hit by Covid-19-related issues. I am not arguing against Rio Tinto shares in general, I just think that Covid-19 might cancel out the benefits of a cheap pound, especially as sterling may not be so cheap after the crisis.Finally, Smith & Nephew is big on knee implants, which are not really a priority right now. It has in any case warned that Covid-19 might hit sales.Shares in GlaxoSmithKline and Johnson Matthey, plus the Mondi share price, might do well in this environment of a cheap pound. Renowned stock-picker Mark Rogers and his analyst team at The Motley Fool UK have named 6 shares that they believe UK investors should consider buying NOW.So if you’re looking for more stock ideas to try and best position your portfolio today, then it might be a good day for you. Because we’re offering a full 33% off your first year of membership to our flagship share-tipping service, backed by our ‘no quibbles’ 30-day subscription fee refund guarantee. Click here to claim your copy now — and we’ll tell you the name of this Top US Share… free of charge! Michael Baxter | Thursday, 19th March, 2020 Our 6 ‘Best Buys Now’ Shares Worried about the falling pound, I would look at these big exporters I’m sure you’ll agree that’s quite the statement from Motley Fool Co-Founder Tom Gardner.But since our US analyst team first recommended shares in this unique tech stock back in 2016, the value has soared.What’s more, we firmly believe there’s still plenty of upside in its future. In fact, even throughout the current coronavirus crisis, its performance has been beating Wall St expectations.And right now, we’re giving you a chance to discover exactly what has got our analysts all fired up about this niche industry phenomenon, in our FREE special report, A Top US Share From The Motley Fool. See all posts by Michael Baxter Simply click below to discover how you can take advantage of this. Michael Baxter has no position in any of the shares mentioned. The Motley Fool UK owns shares of and has recommended GlaxoSmithKline. Views expressed on the companies mentioned in this article are those of the writer and therefore may differ from the official recommendations we make in our subscription services such as Share Advisor, Hidden Winners and Pro. Here at The Motley Fool we believe that considering a diverse range of insights makes us better investors. Enter Your Email Address “This Stock Could Be Like Buying Amazon in 1997” I would like to receive emails from you about product information and offers from The Fool and its business partners. Each of these emails will provide a link to unsubscribe from future emails. More information about how The Fool collects, stores, and handles personal data is available in its Privacy Statement. Image source: Getty Images.