My company is paying for my relocation, 30 days in a hotel plus meals plus car rental plus flight. How can I maximize this in terms of airlines or hotel points ? For example, I have a United credit card and Amex credit card and with my Amex card I get 1% cashback.
At the very least you need to have a Frequent Flyer account with the airline you would be flying with. That allows you go get points regardless of who pays.
Now, if you have the choice between company paying directly and you paying and getting reimbursed than take the latter. This lets you get points for the purchase, so you would have double points.
Cashback are not point. Depending on you flying habits this may be more valuable but for high-value rewards, you can get better than 1% value. That only works if you pay and they reimburse you. You will not get a cashback either.
For the hotel, you can follow the same advice, getting an account with the hotel chain (or parent one) will allow you to collect points for your stay. Some airlines though have an agreement with certain chains of hotels and you can get airline points for your hotel chain.
Having both the flight and hotel add points to the same account will allow you to reach rewards faster. It will also avoid you having to watch more accounts for expiry, unless of course one of those is with an airline or hotel chain whose points do not expire.
Repeat above advice for cars. It is very common for car rental companies to be able to credit points into a frequent flyer account. Choose the car rental company according to which one has can credit points into the frequent flyer program of your choice.