Can I use the helping verb can in the future? "I can travel to London tomorrow." Or I have to use able to? "I am able to travel to London tomorrow."
'Can' is perfectly fine in this context, though it is often used in a 'reserved' manner, by which I mean that someone might well say "I can travel to London tomorrow, (but really don't want to.)"
'Can' is not a direct replacement for 'Able to' in all circumstances - it works fine in your example, but to borrow Michael H's example, "You can drive my car" does not mean the same thing as "You are able to drive my car"
English doesn't really have a Future Tense anyway, but I would say that in I can go tomorrow, can is effectively Present Tense. You can see this at the syntactic level by noting that the "future" version of I can go is I will be able to go.
But it's also true at the semantic level, in that I can go tomorrow effectively means My current status is that I will be able to go tomorrow. That "present tense reference to future ability" may be more obvious if we also consider negating contexts...
[My mother's dementia is getting worse...]
1: ... I hope she will be able to recognise me next Christmas
2: ... I'm afraid she won't be able to recognise me next Christmas (won't = will not)
3: ... I hope she can recognise me next Christmas (QUESTIONABLE - see below)
4: ** I'm afraid she can't recognise me next Christmas (INVALID)
Most native speakers would accept the "Present as Future" usage in #3 - particularly if extended to ...can still recognise me (which more overtly references the passage of time between now and next Christmas).
But note that most native speakers would not accept #3 if we change I hope... to The doctor says... That's because my specific example refers to [future] ability. In a structurally / syntactically identical example where the meaning is more about [present / future] permission, there's no real difference between...
5: The doctor says I can go home tomorrow
6: The doctor says I will be able to go home tomorrow
Because it's both a "defective" verb (with an incomplete conjugation) and a "modal" (auxiliary verb expressing necessity or possibility), can is a difficult word to master in English. There's too much to cover in a single Answer here on ELL, but I'll just point out that in most contexts, the meanings of...
7: The doctor said I can go home tomorrow
8: The doctor said I could go home tomorrow
...are identical. But sometimes, #8 means ...might be able, not ...will be able or ...will be permitted.